China has called on US President Donald Trump to veto legislation aimed at supporting Hong Kong's pro-democracy protest movement, warning it will retaliate if the Congress-backed bills become law.

Chinese foreign ministry spokesman Geng Shuang on Thursday said the Hong Kong Human Rights and Democracy Act undermined Beijing's interests in the semi-autonomous territory, which has been rocked by months of anti-government demonstrations.

The act mandates sanctions on Chinese and Hong Kong officials who carry out human rights abuses and requires an annual review of the favourable trade status that Washington grants Hong Kong.

Another bill prohibits export to Hong Kong police of certain non-lethal munitions, including tear gas, pepper spray, rubber bullets, water cannon, stun guns and tasers.

"We urge the US to grasp the situation, stop its wrongdoing before it's too late, prevent this act from becoming law [and] immediately stop interfering in Hong Kong affairs and China's internal affairs," Geng said at a daily news briefing.

"If the US continues to make the wrong moves, China will be taking strong countermeasures for sure," he added.

Geng's comments came after the US House of Representatives overwhelmingly approved the bills on Wednesday, a day after the Senate passed them on voice votes.

The bills have now been sent to the White House for Trump's consideration. White House officials have indicated that the US president will sign-off on the measures.

If they become law, the tension between Washington and Beijing is likely to increase, casting a shadow over delicate talks aimed at ending the continuing US-China trade war.

Hong Kong's government, for its part, has also expressed its strong opposition to the legislation saying it would damage the territory's relations with the US.

"The two acts will ... also send an erroneous signal to the violent protesters, which would not be conducive to de-escalating the situation," the city government said in a statement on Thursday.

The financial hub has already been pushed into a recession by the continuing turmoil.

Months of unrest

Hong Kong's nearly six months of protests began in opposition to proposed legislation that would have allowed criminal suspects in the city to be extradited to face trial in mainland China, where critics say their legal rights would be threatened.

While Hong Kong leader Carrie Lam has since withdrawn the bill, demonstrations have continued unabated with calls for greater freedom and China to honour the "one country, two systems" framework that was the basis of Hong Kong's handover to China from Britain in 1997.

Beijing promised Hong Kong a "high degree of autonomy" for 50 years when it regained sovereignty over the territory, but protesters say freedoms have since steadily eroded.

The unrest has marked the most serious popular challenge to Chinese President Xi Jinping since he came to power in 2012.

Millions of angry citizens have taken to the streets in giant marches, and protesters have repeatedly clashed with police, who have frequently used tear gas and water cannon against those demonstrating.

In the past two weeks, protesters have torched buildings and infrastructure, including a footbridge, mass transit stations and toll booths at the city's Cross Harbour Tunnel linking Hong Kong island to the Kowloon peninsula.

The protesters say they are angry at the way the MTR, Hong Kong's public rail network, has helped riot police, and that shutting down key infrastructure forces the government to listen to their demands for universal suffrage and an independent inquiry into police violence, among other things.

University standoff continues

The protests in recent days have meanwhile, been focused on the campus of the Hong Kong Polytechnic University, with fiery clashes that saw police fire tear gas and rubber bullets at protesters, who in turn shot arrows and lobbed Molotov cocktails back at the officers.

Al Jazeera's Scott Heidler, reporting from Hong Kong, said despite "several students" having left the facility over the last 24 hours, a contingent of about 100 protesters remain holed up inside.

"Word is coming out from protesters still in the university itself ... they say they are still standing strong," Heidler said.

The site, in the centre of the bustling Kowloon peninsula, is the last campus still occupied by activists during a week that saw some of the most intense violence since the anti-government demonstrations erupted in June.