Beijing on Friday denounced what it called "violent interference" by US lawmakers critical of what they see as a worsening human rights environment in Hong Kong.
Congressional representatives introduced the "Hong Kong Human Rights and Democracy Act", which appears designed to put pressure on the city - and its pro-Beijing leader - to withdraw a planned extradition law.
The bill threatens to remove Hong Kong's status as a US special trading partner.
Some US lawmakers have "made irresponsible remarks about Hong Kong affairs and violently interfered in China's internal affairs", said Chinese foreign ministry spokesman Geng Shuang at a press briefing.
"Relevant people in the United States (should) abandon the illusion of attempting to mess up Hong Kong," he added.
Tens of thousands of demonstrators have taken to the streets of the semi-autonomous city this week to protest a deeply unpopular plan to allow extraditions to China.
Critics say the law would be abused by an increasingly assertive Beijing to pursue its political enemies.
On Wednesday, the international finance hub was rocked by the worst political violence since before its 1997 handover, as riot police fired tear gas and rubber bullets at protesters.
Dozens were injured in the clashes, which have fuelled public anger and sparked accusations of police brutality. Another mass rally is planned for Sunday.
The city's pro-Beijing leader Carrie Lam, who is facing mounting pressure to abandon the extradition legislation, has so far refused to meet protester demands to withdraw or scrap the bill.
"China's determination and will to uphold national sovereignty, security and development interests are unflinching," Geng said.
"We are not afraid of any threats and intimidation," he said. "Any vain attempts to create chaos in Hong Kong... will surely be met with the opposition of all Chinese people, including the vast number of Hong Kong compatriots."