China's foreign ministry said it would take "firm counter measures" - accusing the USA of "sinister intentions".
Trade negotiators from Washington and Beijing are trying to defuse their ongoing tariff war.
"Without question, the American people support the people of Hong Kong, and this law makes that abundantly clear to Hong Kongers, the global community, and the Chinese Communist Party", said Senators Jim Risch, chairman of the Senate Foreign Relations Committee.
The Hong Kong and Macao Affairs Office, Beijing's top body in the city, called the USA the "biggest black hand".
Pro-democracy protesters held a Thanksgiving Day rally to thank the United States and President Trump for signing bills into law on Wednesday that support the demonstrators in their struggle against Beijing. "They are being enacted in the hope that leaders and representatives of China and Hong Kong will be able to amicably settle their differences leading to long term peace and prosperity for all".
What does the law say?
Protests have been happening there for many months.
Trump distances himself from Giuliani's Ukraine efforts
Speaking in Ukrainian, Lutsenko said that Giuliani at first agreed he could help make the connection but that he never did. And top diplomats have testified that Giuliani's role loomed large over their own official operations regarding Ukraine.
On July 18, the EU Parliament adopted a resolution on the situation in Hong Kong calling for, among other measures: "the EU, its Member States and the worldwide community to work towards the imposition of appropriate export control mechanisms to deny China, and in particular Hong Kong, access to technologies used to violate basic rights".
Gao Feng, a spokesperson for China's Commerce Ministry, did not comment directly on whether the Hong Kong law would affect trade talks, saying there were no new details of their progress to disclose.
All democracies are concerned about Hong Kong's situation, Tsai said on the sidelines of an event in Kaohsiung, adding: "Hopefully, Hong Kongers will persevere in their pursuit of democracy, while the Hong Kong government should deal with people's appeals for democracy and freedom". Seen as a stunning rebuke to Beijing and its supporters in Hong Kong, the elections drew a record turnout in voter participation.
Hong Kong is grappled in the protests since June with people hit the street against the Chinese backed government.
It was unclear whether any protesters remained on the campus as about 100 plainclothes police moved in to collect evidence and remove unsafe items such as petrol bombs.
British Columbia MP Kenny Chiu, who represents a Vancouver-area riding for the Conservative Party, offered his support for Ms. Siu in a video message from Hong Kong Wednesday where he volunteered as an election observer for local district votes that produced a landslide victory for pro-democracy candidates.
On Thursday, authorities moved into the Polytechnic University days after it had been the site of a fierce standoff between student activists and riot police.
Police officials said they were not searching for any protesters that may be still holed up on campus.
A senior police official, Chow Yat-ming, said the focus of the operation was not to arrest anyone but to remove hazardous items that were a threat to public safety, and to gather evidence of "malicious" damage to campus facilities.