Meanwhile the Federation of Students makes a plea for food and water donations as they are running short on supplies for the night. Protestors leaving the area hand them bottled drinks and bags of snacks, while thanking them for their help.

11.16pm: Organisers say the number of people who took part in the July 1 march was 510,000. The figure is in stark contrast to the 'official' police tally of just 92,000.

Watch: Protestors gather at Chief Executive's Office to continue protest

11.05pm: Dozens of protesters reach the Chief Executive's office in Tamar, where scores of police are manning barriers.

Occupy Central Benny Tai Yiu-ting said he understood many people would be staying out for the night and that, having been a student leader himself many years ago, he "felt a sense of pride".

"I am confident all student and citizens will uphold a non-violent spirit. Before the work day starts I am sure the protesters will leave," he said, adding that there was no need for police to "clear the area and use any violence". "If police try to clear area, try to use violence on students, I can assure you that you will bear even more serious political consequences," he warned.

10.52pm: Some 50 journalists are waiting outside the Chief Executive's Office in Tamar. Members of student group Scholarism are expected to arrive any time to stage a sit-in. The group has not obtained a letter of no objection from the police.

Separately a SCMP reporter said it took more than three-and-a-half hours to complete the full July 1 march from Victoria Park to the final destination in Central, walking along at the pace of the crowd without taking any short cuts.

10.39pm: Protesters in Chater Road applaud as members of student-led group Scholarism set off for the Chief Executive office in Tamar, where they are planning an 'occupy' protest. 

10.34pm: And still the march goes on! The tail of the original July 1 demonstration is approaching Admiralty, more than seven hours after the first marchers set off from Victoria Park.

10.30pm: Lawmakers Lee Cheuk-yan (Labour Party leader) and Albert Ho Chun-yan (former Democratic Party leader) pledge to remain in Chater Road to back the students' 'occupy' action.

10.14pm: Kay Tse’s controversial new Canto-pop song 'Egg and Lamb', which was uploaded on YouTube on June 30, has so far attracted more than 270,000 views. The song talks about how a free man turned into a slave, and how “eggs crash into wall” refusing to yield.

Pop singer Hocc, who is an outspoken gay rights advocate, has uploaded a picture of her joining the protest with fellow singer Anthony Wong Yiu-ming onto her Facebook page. The picture has drawn more than 15,000 'Likes' in six hours.

10pm: Scholarism activist Joshua Wong Chi-fung tells the SCMP how a uniformed policeman pushed him to the ground at about 6pm on Yee Wo Street when he was asking police why they were setting up more barricades there.

"I was asking them for an explanation peacefully and was not attempting to push the barricades off. But an officer ordered me to leave the demonstration zone immediately. He then pushed me on my chest and I fell onto the ground," 17-year-old Wong said.

9.56pm: Student-led group Scholarism leaders, Oscar Lai Man-lok and Joshua Wong Chi-fung, appear onstage in the Chater Road rally. Wong says he is prepared for the pepper sprays which might be used by police against their occupy action.

Chow Yong-kang, Secretary-General of Hong Kong Federation of Students, calls on Hongkongers to back their civil disobedience action. "Without the support of Hongkongers, I am sure police would take swift or even violent action to clear the scene," he said.

9.36pm: Speeches and proclamations are coming thick and fast as group leaders try to keep demonstrators motivated.

Johnson Yeung Ching-yin, convenor of the Civil Human Rights Front, said the city did not need to take orders from the "dictatorship thousands miles away". "Tonight, [the young people] would kick off the prologue of the fight ... our fate should be decided by the people, but not Leung Chun-ying, [development chief] Paul Chan Mo-po and the central government," he said.

Civic Party barrister Tanya Chan, a former legislator and rally host, urged the police on duty tonight to show restraint. "We might look like standing on the opposite sides today, but afte rall, you are also Hongkongers," she said. "What actions you take against the protesters tonight might affect the city's future."

The hosts also briefed the protesters on the principles of non-violent resistance, such as not hitting back and being friendly to police.

9.28pm: Civic Passion leader Wong Yeung-tat tells the Post: "We will start a rally outside Wanchai Methodist church after the tail has passed by. And we will see how the students sit-in goes and decide what are we going to do."

The League of Social Democrats' vice chairman Avery Ng Man-yuen says some League members will join the students' protests, although the League will not stage a demonstration of its own tonight.

9.10pm. Chater Road is occupied. Hundreds of students are sitting in the road under the glare of spotlights, stretching back several hundred metres. It is unclear how long they will stay or whether police will move them on. The protest was organised by the Federation of Students and Scholarism and was billed as a practice run for Occupy Central.

Another loud hiss from the crowd as one of the rally organisers reads out the government's statement on the march, which once again said public nomination would not be allowed - one of the key demands of protesters.

8.55pm: Thousands of people join a rally at Chater Road, extending from Jackson Road to Ice House Street.

Police say they will take decisive action to ensure law and order and public peace are maintained. Senior superintendent of Police Public Relations Branch, Kong Man-Keung, said the force had not issued a notice of no objection in relation to the planned sit-in by students in Chater Road after the march.

He said such activities at night may be dangerous as people gather in dim light. He urged demonstrators to follow police instructions and take part in the rally peacefully, adding that media reporting the event should also be careful.

"If any activity is posing threat to public safety and order, especially if marches were held at night, light would be insufficient and it will be dangerous - so the police would take action decisively," Kong said.

"I also call for the relevant bodies... to express their demands peacefully and rationally, to keep calm, exercise restraint, and listen to the police's appeals and instructions.

8.45pm: Protesters in Chater Road give out a loud hiss in unison after organisers reveal the official police turnout figure of 92,000. Official figures given by the police and protest organisers usually vary wildly as both sides attempt to score points with high or low turnout figures. Actual figures nornally fall somewhere between the two.

8.30pm: Civic Party barrister Alvin Yeung is briefing protesters on what to do and what rights they have if they are arrested.

Albert Ho Chun-yan of the Democratic Party says he has not seen such a large turnout since the rally in 2003. "It shows Hong Kong people demand real 'one country, two systems,'" he says.

Meanwhile Apple Daily's Facebook page says it has been under severe cyber attack since mid-afternoon. Their site first went down shortly before 3pm, recovered at 5.30pm, and crashed again at 7pm.

8.19pm: Police say 92,000 marchers set off from from Victoria Park today.

Officers say a 22-year-old man was arrested in Causeway Bay for vandalism when he threw a metal barrier at a bus.

8.05pm: Hundreds of protesters have gathered at Chater Road, where students have pledged to spend the night in rehearsal for Occupy Central. Police say they will give a press briefing at 8.15pm.

Hosts of the rally at Chater Road blasted the police for stationing police cars at Jardine's Bazaar which blocked marchers from proceeding.

Singer Denis Ng led the protesters singing the cantonese version of "Do you hear the people sing?"

7.40pm: There are reports a convenor of the student activist group Scholarism, Joshua Wong Chi-fung was assaulted, leaving scratches on his face. Oscar Lai, a member of Scholarism who was alerted to the alleged incident, was unable to confirm the whereabouts and the condition of Wong.

7.37pm: The rally has lasted longer than even organisers expected. As the sky turns dark, street lamps are switched on in Victoria Park. "I have been a master of ceremonies for the march for 10 years," said Lit Ming-wai, an organiser of the annual demonstration. "It is the first time for me to see people still waiting to leave Victoria Park when night falls.

Meanwhile, Cantopop singers Anthony Wong Yiu-ming and Denise Ho Wan-si, who have both come out as gay and been outspoken on many political issues in the past, are cheering for marchers in Causeway Bay near Sogo.Wong said he had been stationed there since 3pm and that he wanted to call for more people to voice their opinions.

"I think Hong Kong is at its worst time now," said Wong. "We need to stand out and tell the government that we need real universal democracy. No one wants to get that far as to occupy Central, but it'll be a special measure in special time."

7.20pm: Four hours after the march kicked off the last batch of participants are walking through Victoria Park, where things all began just after 3pm. Using loudspeakers, organisers thank the last ones for their patience, through sun and rain. Among the last to leave are a group of People's Power members, waving orange flags.

7.06pm: Avery Ng of the League of Social Democrats said chairman "Long Hair" Leung Kwok-hung wanted to join the march but was frustrated by his jail term.

"Treasure the chance you can to march today. Don't let me see you exit and give up when you reach Wan Chai," Ng urged fellow protesters

6.55pm: In its official response to the public procession today, the government says it respects residents' freedom and right of expression and has always encouraged the public to express their views via legal channels and in a peaceful manner.

But in case of any contravention of the law and breach of public order, "law enforcement agencies will handle such a situation strictly in accordance with the law to ensure that law and order and public peace are maintained in Hong Kong", a government statement said.

It reiterated that proposals on political development should be, legally, strictly in accordance with the Basic Law and relevant Interpretation and Decisions of the NPCSC.

Regarding the civic nomination proposal advocated by some groups and individuals, the government said it believes that it is unlikely that such a proposal will be adopted.

It said it had collected different views expressed by different groups and individuals in the community during the five-month public consultation on constitutional development and would "faithfully reflect the views received during the consultation period in the consultation report".

The government is aware that a host of other public aspirations are expressed in today's procession, it added, and will continue its endeavour to tackle various problems including those related to economic development, housing, poverty, ageing society and the environment, it added.

6.34pm: Crowds in Victoria Park are becoming increasingly angry at being hemmed in, with protesters again stopped from leaving. Shouts of 'make way' go up from demonstrators. When the MC on stage providing entertainment asks who voted in the unofficial Occupy Central poll a sea of hands shoots up.

6.29pm: Police warn march organiser, the Civil Human Rights Front, that they may take legal action for failing to heed police instructions. Wan Chai District Commander Leung Sai-kau says: "The organisers’ car that is leading the procession has been progressing very slowly and at times stopped We have repeatedly asked the organisers to keep moving but we were ignored.

"The police expressed extreme disappointment with the un-cooperative attitude of the organisers and may pursue legal liability in accordance with the law.”

Leung also rejects calls by the front to open up the entire Hennessy Road to accommodate the protesters, saying doing so could seriously affect emergency services or other road users.

6.15pm: Mainland shoppers are going about their business in the stores of Causeway Bay despite the hours-long protest outside. Annie Yen of Shanghai, who was looking at dresses on Hennessy Road, said she wasn't fazed by the demonstrators, but opposed divisions between Hong Kong and China.

"Freedom is very important but I think we should unite together," said the doctor, visiting the city for a short holiday and fearing a potential escalation in violence. "We shouldn't do anything to separate from our big family of China," she said. "War is not good. We shouldn't have a war."

6pm: Police make a statement telling organisers the procession is moving too slowly and urging them to speed things up and let the demonstrators proceed as quickly as possible. They accuse organisers of disregarding police advice and warnings and taking too long to complete the designated route.

Countering police accusations, the front's convenor Johnson Yeung Ching-yin says in Admiralty that they are stopping repeatedly because they know that with the bottleneck in Causeway Bay, that there's no way marchers can catch up with the head. Yeung urge police to open more road lanes to increase pedestrian flow.

Outside Sogo department store demonstrators break through a police cordon and spill onto the other side of Hennessy Road, leaving just one lane open to traffic.

In Victoria Park a group of protesters accuse police of trapping them. "Let me out to pee! Why don't you let me out!" one elderly woman yells.

5.46pm: A group of mainland tourists carrying luggage outside Victoria Park look shocked by the road blockage and sea of white t-shirts. They ask protesters what is going on, and when told it is an anti-government rally, say they are amazed by the passion of Hongkongers, although they decline an invitation to join the crowd.

Hong Kong Observatory extends its thunderstorm warning until 6.30pm. Things could get very wet indeed.

5.40pm: The heavens have finally opened in Causeway Bay. The rain is coming down hard, angering protesters who are still being blocked from marching by police. Many are urging police to clear the roads and let them start. Umbrellas are up everywhere and many are seeking shelter under shop awnings.

5.35pm: A group of about 20 gay rights demonstrators gather at Victoria Park, each holding a rainbow-coloured umbrella. Eric Chan Wang-yuen, 28, said he felt gay rights were closely connected to the universal suffrage, because they were both universal values and only a government elected by the people would listen to voices of the marginal.

"I've been joining similar demonstrations every time but I feel the more voices we have the less willing to listen the government has become, which makes me even angrier," said Chan. "If we don't stand out this year, we may not be able to next year. We need to wake up and be responsible for ourselves."

5.20pm: A human traffic jam has snarled up the junction of Jardine's Bazaar and Yee Wo Street, not helped by multitudes of bemused shoppers trying to squeeze their way through the crowds. Hundreds of protesters have been locked in place for over an hour now, with some speculating that police are deliberately using tactics to stem the flow of the demonstration.

Outside Victoria Park people are chanting 'Open up' as police continue to keep roads closed and traffic flowing.

5.05pm: The march is developing a life of its own. In Wan Chai hundreds of demonstrators overtook the march organisers and northeastern New Territories villagers who were supposedly fronting the procession, and struck out for Central alone. By 5pm they had reached the Bank of China Tower and will reach the Chater Road finish point soon.

Civic organisations and political parties booths line the route.

SCMP reporters on the ground say they have never witnessed anything like it before.

4.56pm: The rain has started - bringing relief to many along the route. The head of the march has already reached Pacific Place and still there is a seemingly endless stream of protesters pouring off the Tin Hau MTR and patiently queueing up to get started (are they going round again?).

Police are telling them the park is full and now Tin Hau is filling up. Were the organisers right about a possible 500,000 turnout?

Marchers in Yee Wo Street, Causeway Bay, are urging police to clear the roads and let them through.

4.38pm A girl faints in the stifling heat of Victoria Park. Crowds make way for medics as friends put a bag under her head. It's nearing 5pm and the temperature has just dipped below 30C.

4.25pm: Huge crowds are still trying to get into Victoria Park at the Tin Hau end, despite the protest having been underway for well over an hour. The streets of Causeway Bay are awash with demonstrators. Some of those in the park are complaining that police are using the traffic flow outside to hem them in.

4pm: At Hennessy Road near Morrison Hill, members of a local arts troupe, FM Theater Power, spread a blanket on the road of title pages from the white paper, sprinkled with water and antiseptic solution to look like blood blotches. "What it says violates one country, two systems," said Tsang Lok Sze. Fellow actor Fung sai Kuen stomped his foot on the ground. "It steps on one country, two systems!"

3.55pm: Anson Chan Fang On-sang, former chief secretary, joins the march with members of her think-tank Hong Kong 2020.

"I appreciate the students' courage but I call for restraint on all sides, including the students and police," she said, when asked whether she supported the students' plan to rehearse Occupy Central sit-in tonight.

Chan also called for sincerity in the central and local governments in negotiating the electoral reform to give Hong Kong people a genuine choice in candidates in the 2017 chief executive election.

3.45pm: To give an idea of the police presence in the city this afternoon, there are officers stationed every few metres on both sides of Hennessy Road outside the Sogo store in Causeway Bay, awaiting the arrival of the first demonstrators.

3.23pm: And they're off! The march has officially started, albeit a little late. The far end of Victoria Park remains at a standstill, with people still queuing to get in, but a great swell of people is on the move under grey skies.

3.16pm: The crowd is becoming impatient at the Tin Hau end of Victoria Park, with people climbing over railings to get in. there's live singing onstage in the park, while elsewhere, as far afield as Wan Chai, sporadic outbursts of Do You Hear The People Sing can be heard.

3.10pm: Marchers of all ages are taking part today. Tom Shum, 40, is taking part with his wife and two young daughters - aged just five and two years. "My older daughter didn't want to come as she said it's so hot today but I tell her we have to come to protect our city," Shum, an advertising worker, said. He said his family were spurred to attend by the proposed new towns development in the New Territories.

Chuk Ka-man, 31, said the time has comefor Hongkongers to speak up. "If we don't come out and say something now, we won't be able to do it in the future," she said.

Sou Ka-hou, of Macau Conscience, a pro-democracy group, said he came to the march to support public nomination for Hong Kong people. "If Hong Kong people don't have this, we in Macau will also be doomed," he said.

2.58pm: All of the football fields and the lawn are now open, according to a public announcement. The park is a sea of umbrellas and fans as sweltering protesters battle to keep the sun at bay. This time last year it was a very different picture as marchers were getting drenched as a T3 typhoon warning was in force.

2.50pm: Organisers say two of Victoria Park's football fields are full and protesters are being herded into other areas of the park. One of the six fields at the Tin Hau end of the park is still almost empty, but heavy congestion appears to have brought things to a standstill. The streets of Causeway Bay are filling up and the volume is increasing.

2.27pm: Beijing's white paper and CY Leung's portrait this morning became the first casualties of the day, when both were burnt by protesters demanding public nomination of the chief executive in 2017. In a speech CY said the city’s residents should avoid doing anything that might damage Hong Kong’s “prosperity and stability". But will they heed his words this afternoon?

2.10pm: The police deployment of 4,000 officers to the streets of Hong Kong for today's march is the largest the city has seen since the World Trade Organisation's ministerial conference in December 2005, when anti-globalisation activists from around the world flocked to the city. 

1.55pm: Burning issues on the 17th anniversary of the handover of Hong Kong include Occupy Central’s unofficial referendum on the election of the chief executive in 2017, Beijing’s recently released white paper and the building of new towns in the New Territories. The Observatory has issued a Hot Weather Warning, with temperatures currently touching 31C.

1.45pm: With an hour-and-a-quarter to go until the annual July 1 march kicks off, much of the city remains quiet, but preparations are underway at both ends of Hong Kong. There's a carnival atmosphere in Victoria Park as thousands of marchers gather and protesters yell slogans through loudhailers, while workers in Central are busy erecting water barriers. A number of shops on Chater Road, where the march ends, have already closed their doors, including luxury stores Chanel and Cartier. Other stores, including Prada and Armani, are closing early.