Chinese President Xi Jinping has effectively neutered the most democratic institution under China's rule, sending a message to Joe Biden that no amount of pressure will prompt him to tolerate dissent against the Communist Party.

China's top legislative body on Wednesday passed a resolution allowing for the disqualification of any Hong Kong lawmakers who aren't deemed sufficiently loyal. Chief Executive Carrie Lam's government immediately banished four legislators, prompting the remaining 15 in the 70-seat Legislative Council to resign en masse hours later at a joint press briefing.

“This move makes it clear that dictatorship has descended onto Hong Kong and that Chinese Communist Party can eradicate all opposing voices in the legislature,” Fernando Cheung, one of the lawmakers, told Bloomberg News.

“There's no more separation of powers, no more 'one country, two systems', and therefore no more Hong Kong as we know it.”

The resolution is the latest sign of China's determination to rein in dissent in the wake of anti-government protests last year calling for meaningful elections in the semi-autonomous territory.

Beijing has since passed a series of measures asserting greater control over Hong Kong, first targeting democracy activists who hit the streets and now going after dissenters in democratic institutions set up under British colonial rule.

Beijing has already shown disdain for the Legislative Council, bypassing it in June to impose sweeping national security legislation that undercut the “one country, two systems” framework that had long attracted investors to the financial hub.

The Group of Seven nations accused China of violating the terms of its handover agreement with the UK, while the Trump administration revoked many special privileges granted to the city and sanctioned more than a dozen senior officials who oversee the territory.

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Biden's win presents an opportunity to reset relations between the world's two biggest economies, even though the former vice-president called Xi a “thug” on the campaign trail and has vowed to “fully enforce” laws punishing Beijing for eroding Hong Kong's autonomy.

Yet China's move on Wednesday doesn't leave him many options for a detente, particularly given how the city has long sat at the crossroads of western democracy and Communist rule.

“With this decision, China shows that it doesn't care about the West, about the US,” said Jean-Pierre Cabestan, a professor at Hong Kong Baptist University's government and international studies department, who has written several books on Chinese politics and foreign policy.

“It's going to be very hard for Biden to relax the US policy on China and Hong Kong. How can you relax the sanctions? It's a very sad day for Hong Kong.”

The decision of the National People's Congress Standing Committee is “conducive to the long-term peace and stability, as well as prosperity and development of Hong Kong,” Chairman Li Zhanshu said at the close of its two-day meeting.

Offences included supporting Hong Kong independence, refusing to recognise China's sovereignty over the city, asking foreign countries to intervene, failing to uphold the territory's Basic Law or pledge allegiance to Hong Kong and “engaging in any other acts that endanger national security”, said Lam, Hong Kong's leader.

“We need to have a political body that's composed of patriots,” Lam said at a briefing on Wednesday, echoing similar statements from China's top agencies overseeing Hong Kong.

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She dismissed concerns that Hong Kong would have a “rubber-stamp” legislature if the pro-democracy members resigned, saying she welcomes "diverse opinion”.

The Hang Seng Index closed 0.28 per cent lower on Wednesday, with declines accelerating in late afternoon trade.

The lawmakers disqualified Wednesday – Alvin Yeung, Dennis Kwok, Kwok Ka-ki and Kenneth Leung – were among the body's more moderate members, and not known proponents of independence.

They were among 12 candidates barred in July from seeking election for, among other things, vowing to “indiscriminately” vote down legislative proposals, a reference to the opposition's plan to exercise a constitutional provision that would force Lam to resign if her budget failed to pass.

Pressed on whether she was seeking to ban parliamentary delay tactics common to legislatures around the world, Lam said “it's all a matter of degree” and pledged to “respect the check-and-balance responsibility” of the body.

“They want to turn the Legislative Council into the National People's Congress,” pro-democracy lawmaker James To said as the opposition vowed to resign at an evening briefing on Wednesday. Lawmakers held hands and chanted protest slogans, including “Hong Kong add oil – together we stand”.

Prior to the decision, the Hong Kong government had postponed an election for the Legislative Council for a year citing coronavirus concerns. The decision on Wednesday means that authorities will now be able to effectively oust any lawmakers who stand in the way of Beijing's agenda, according to Antony Dapiran, a Hong Kong-based lawyer and author of City on Fire: The Fight for Hong Kong.

“It means, effectively, the end of meaningful opposition in Hong Kong and the acceleration of the integration of Hong Kong into the mainland party state,” he said.

China warned other countries to avoid commenting on the moves, with Foreign Ministry spokesman Wang Wenbin on Wednesday calling the matter “purely China's internal affairs”. He warned foreign governments to avoid “interference or wanton comments”.

In Hong Kong, pro-democracy lawmakers said they would keep fighting for political freedoms even while leaving the legislature.

“You may think we have lost the fight, but I can tell you that it's absolutely not true,” Lam Cheuk-ting, one of those who stepped down, said. “No matter what position you're in, as long as we Hong Kong people persevere, history tells us that authoritarianism would finally come to an end one day.”