US Congress should immediately stop interfering in Hong Kong affairs and advancing Hong Kong-related acts, the Foreign Ministry's top representative in the Hong Kong special administrative region said in a statement on Thursday.

Hong Kong affairs are China's internal matters and US interference is a grave violation of law and international relations norms, the ministry representative said.

The statement came after the US Senate Foreign Relations Committee and the House Foreign Affairs Committee have marked up and passed acts including the "Hong Kong Human Rights and Democracy Act 2019".

The Office of the Commissioner of the Chinese Foreign Ministry in Hong Kong expressed strong disapproval of and firm opposition to these US politicians' disregard for facts and basic norms of international relations.

The office further slammed the serious interference in China's domestic affairs.

The office pointed out that the policies of "one country, two systems", "the people of Hong Kong governing Hong Kong" and a significant degree of autonomy have been fully implemented in strict accordance with the Constitution and the Basic Law in Hong Kong since its return to China.

Certain US congressmen, however, have shamelessly meddled with Hong Kong affairs by making groundless accusations concerning human rights and democracy, and openly cheered the anti-China troublemakers in Hong Kong and violent radicals, the office said.

This only proves again that they are the "black hands" behind the scenes, the office said.

They're bent on advancing acts for their selfish political interests and are standing on the opposite side of not only Chinese people, including our Hong Kong compatriots, but also all international businesses and citizens in the city, the office said.

This will inevitably backfire and undermine US interests here, the statement said.

The office stressed that Chinese people will not be intimidated by any external pressure or coercion and that any plot to mess up Hong Kong is doomed to fail.

"We will never sit idly by to let foreign interference run wild. We urge the American congressmen to immediately stop playing with fire in advancing Hong Kong-related acts, which will only get themselves burned," the statement said.