Hong Kong's leader accused the United States on Tuesday of applying "double standards" in its response to violent protests as she warned Washington's plan to place trade restrictions on the financial hub would "only hurt themselves".

Semi-autonomous Hong Kong has been rocked by months of huge and often violent pro-democracy protests over the past year, which riot police have stamped out with more than 9,000 arrests.

Washington has been critical of Hong Kong's response to the demonstrations with US President Donald Trump last week vowing to end the city's special trading status after Beijing announced plans to impose a sweeping national security law on the business hub.

On Tuesday, Hong Kong's Chief Executive Carrie Lam said such a move would be self-defeating as she took aim at the Trump administration for its own response to violent racial justice protests sweeping the United States.

"We have seen most clearly in recent weeks the double standards that are around," Lam, who was selected as city leader by a pro-Beijing committee, told reporters.

"You know there are riots in the United States and we see how local governments reacted. And then in Hong Kong, when we had similar riots, we saw what position they adopted then."

Both Chinese and Hong Kong officials have seized on the unrest gripping the US in their propaganda drive to justify their own crackdown on pro-democracy protests and the national security law plans.

Last week, China's rubber-stamp parliament approved the plans for a law that would punish secession, subversion of state power, terrorism and acts that endanger national security -- as well as allow Chinese security agencies to operate openly in the city.

Beijing says the anti-subversion law -- which will bypass Hong Kong's legislature -- is needed to tackle "terrorism" and "separatism".

Opponents fear it will bring mainland-style political oppression to a business hub supposedly guaranteed freedoms and autonomy for 50 years after its 1997 handover from Britain to China.

Hong Kong's Chief Executive Carrie Lam accused the United States of 'double standards' in its response to violent protests
Hong Kong's Chief Executive Carrie Lam accused the United States of 'double standards' in its response to violent protests AFP / Anthony WALLACE

Lam's office said she and key security officials will make a one day visit to Beijing on Wednesday to discuss the legislation with central authorities.

At Tuesday's weekly press conference, Lam said Hong Kong had spent 23 years failing to enact its own national security laws in the legislature, prompting Beijing to take the initiative.

"There is simply no justification whatsoever for any government, any economy, to impose sanctions on Hong Kong as a result of a very legitimate process of the central government, the central authorities, taking this decision to enact laws for Hong Kong to better protect national security," she said.

"They will be hurting their own interests in Hong Kong," she added, referencing US threats to restrict trade privileges.

Lam said some 1,300 American businesses have a presence in the financial hub, which generates the largest trade surplus for the US compared to any other country or territory, she added.

She also said Hong Kong allows Americans to enter without a visa, a privilege that is not reciprocated.

Lam did not elaborate on whether visa-free travel could be rescinded in response to any trade sanctions but Chinese officials have vowed to implement "counter measures" to any move by the US.

Under a 1992 law, the US treats Hong Kong as a separate trade entity to the more restricted and authoritarian Chinese mainland as long as the city retains key freedoms and autonomy.

Last month the State Department announced the territory was no longer sufficiently autonomous to justify that special status.