She, alongside lawmakers Dennis Kwok and Charles Mok, are in the midst of a 10-day trip to the US at the invitation of the White House. Their visit included a face-to-face meeting with US Vice-President Mike Pence at the president’s official residence and discussions with members of the National Security Council.

Among the concerns they flagged to the White House, Chan said, was the government’s recent proposal to allow the reciprocal handing over of fugitives to mainland China and any jurisdictions with which the city lacks an extradition deal.

Chan said the trio’s fears were shared by the legal profession, human rights activists and chambers of commerce. The latter group is worried that the arrangement would make the city no longer a safe place to do business, she said.

“I urge all those who support ‘one country, two systems’ and who do business in Hong Kong to monitor very carefully developments on this front and to speak up before it is too late,” Chan said, adding that the faithful implementation of the city’s guiding principle matters to the US and liberal democracies everywhere.

“Talk to government officials, politicians and business interests, and the average man in the street and please, please speak up when things are not right,” she said.

Referring to pro-democracy protests carried out in 2014 by Hongkongers demanding universal suffrage, she said: “Don’t just wait for another ‘umbrella movement’. Just keep shining a light on Hong Kong.”

The city’s government and Beijing both have pushed back vigorously against any perceived attempts by foreign governments and other external entities to bring pressure to the political situation in Hong Kong.

Following a previous visit by Chan to the US last year, when she met various US political figures and was honoured for her continued political advocacy work by Arizona State University, the Office of the Commissioner of the Foreign Ministry in Hong Kong condemned any “Hong Kong individual interacting and colluding with foreign forces”.

It suggested Chan was attempting to “slander and smear” the one country, two systems principle.

Chan told the Post on Saturday that she believed that by coming to the US to engage with government officials, lawmakers, lawyers and scholars, she was “doing the work that our SAR government should be doing”.

She called on Hong Kong’s leaders to be more proactive in persuading their allies that Beijing was not leading the city.

Ahead of Chan’s Monday remarks at the Heritage Foundation, the trio met representatives of the US-China Economic and Security Review Commission (USCC), a congressional body set up in 2000 to advise lawmakers on the national security implications of the US-China economic and trade relationship.

The trio said the USCC was “very concerned” with the city’s situation, in particular the proposed amendments to the Fugitive Offenders Ordinance.

“They inquired about the government’s proposed amendments … and expressed the worry that the amendments could subject US citizens and business representatives living in or passing through Hong Kong to trials in mainland China where criminal justice is dubious,” the trio said in a statement.

They also discussed whether the “Greater Bay Area” scheme could affect the core values of Hong Kong, and the issues of press and internet freedom during the meeting.

The USCC last November recommended reviewing the arrangement under the US-Hong Kong Policy Act, which has given the city a special status – to be treated separately from mainland China – on matters of trade and economic policy since 1992.

It warned that Beijing’s “encroachment” on the city’s political system could diminish its standing as a global business hub.

The trio said the USCC planned to visit the city in May.

Chan, Mok and Kwok will travel to New York on Wednesday to meet representatives of the city’s Bar Association and members of the Council on Foreign Relations.

Additional reporting by Owen Churchill