“The dictatorial government is using violence to disperse the people’s movement,” said Tattep Ruangprapaikitseree, one of the protest leaders.

Until now, police had not used major force to suppress peaceful protests that have drawn tens of thousands of people, although more than 40 demonstrators - including several leaders - have been arrested in the past week.

Reuters journalists said water turned on the protesters contained chemicals making them sting. Organisers told protesters to disperse more than three hours after they gathered.

“It’s clear that Prayuth sees the people as the enemy. And we him,” protest leader Panupong “Mike” Jadnok told the crowd.

“I have to fight for my future,” said Pin, 22, a university student who declined to give her full name for fear of reprisals.

Protesters also want a new constitution, to replace one drafted under military rule.

“I’m not quitting,” Prayuth told reporters after an emergency cabinet meeting.

“The government must use the emergency decree. We have to proceed because the situation became violent … It is being used for 30 days, or less if the situation eases.”

He warned people not to violate the emergency measures, saying: “Just wait and see … If you do wrong, we will use the law.”

Calls have also built up among protesters for reforms to the monarchy, which is accused by protesters of helping to entrench decades of military influence in politics.

Protests have been largely peaceful.

On Friday, activists Ekachai Hongkangwan and Paothong Bunkueanum were arrested under a law covering violence against the queen for their alleged part in the heckling of the motorcade. They could face life in prison if convicted.

Ekachai is a veteran activist who has been physically attacked several times, in apparent response to his criticism of the military. Paothong, a university student, has been involved in organising the protests.

“We were not notified by the police of the upcoming royal motorcade in which we had no way of knowing because they were not informing us,” Paothong told reporters on Friday.

“Once we knew that there was a motorcade of the queen and the heir presumptive to the throne, I tried to break away from the line and use my megaphone to have everyone move away from the police barriers so the motorcade can pass through easily,” he said.

Demonstrators have denounced the emergency measures and the arrest of some 40 protesters in the past week.

The UN High Commissioner for Human Rights was concerned about the situation in Thailand, said Ravina Shamdsani Said, a spokeswoman for commissioner Michelle Bachelet.

“We are particularly concerned about the application of serious charges, including the crime of sedition, against individuals for peacefully exercising their fundamental rights,” she told a briefing in Geneva.

Parliamentary opposition parties also condemned the emergency measures.

“Puea Thai party calls on General Prayuth Chan-ocha and the state officials to lift the emergency decree and to stop intimidating the people in all manners and to release those who were arrested immediately,” said the party, which has the most seats in parliament.

The Ministry of Digital Economy, meanwhile, announced it would file complaints with police covering five Twitter accounts and five Facebook accounts inviting people to attend Friday’s rally. Such posting could be deemed illegal under the state of emergency, as well as other laws.

Additional reporting by Associated Press