The House of Representatives on Wednesday also passed the bill without opposition, a rare example of overwhelming bipartisan support reflecting concern over the erosion of the autonomy that had allowed the former British colony to thrive as China's freest city and an international financial center.

The United States and China have been at loggerheads for months over the handling of the coronavirus pandemic and Beijing's harsh response to protests in Hong Kong. Washington has also sought to put more pressure on China over mistreatment of Muslim Uighurs in the Xinjiang region.

"This is an urgent moment. Our timing could not be more critical," said Democratic Senator Chris Van Hollen, a lead sponsor of the "Hong Kong Autonomy Act," in a Senate speech urging support for the legislation.

"Through this bill, the US Senate makes clear which side we are on," said Republican Senator Pat Toomey, a co-sponsor.

The bill calls for sanctions on Chinese officials and others who help violate Hong Kong's autonomy, and financial institutions that do business with those who are found to have participated in any crackdown on the city.

Lawmakers said it raced through Congress this week because of China's recent actions, and to show support for protesters in Hong Kong. Thousands gathered in Hong Kong on Wednesday to demand independence, risking steep prison terms as China said Washington should stop interfering in Hong Kong affairs.

'Upping their game'

Elizabeth Rosenberg, a sanctions expert at the Center for a New American Security, called the bill "a very strong step," adding, "They're really upping their game and trying out some very powerful new economic tools."

Hong Kong returned to Chinese rule in 1997 under a "one country, two systems" formula that protected its freedoms, including wide-ranging autonomy. But China on Tuesday introduced sweeping national security legislation for the city, condemned by the United States, Britain and other Western countries.

British Foreign Secretary Dominic Raab reprimanded HSBC and other firms on Wednesday for supporting the law, saying the rights of Hong Kong should not be sacrificed for bankers' bonuses.

Senior British and US politicians criticized HSBC and Standard Chartered last month after the banks backed the new law.

The Chinese security law, which punishes crimes of secession, subversion, terrorism and collusion with foreign forces with up to life in prison, will see mainland security agencies in Hong Kong for the first time and allows extradition to the mainland for trial.

Chinese Foreign Ministry spokesman Zhao Lijian, speaking in Beijing, warned the United States against signing or implementing the bill approved Thursday.

"Otherwise China will resolutely and forcefully resist," he said.

The White House did not respond to a request for comment on whether Trump would sign the bill.

Fellow Republican Toomey said he had "no doubt" Trump would sign it and that it would be properly enforced. Although the measure allows the president not to impose the mandatory sanctions for national security reasons, it also allows Congress to vote to disapprove if lawmakers feel Trump is misusing the waiver provision.

The United States has already begun eliminating Hong Kong's special status, halting defense exports and restricting the territory's access to high-technology products.