All of Hong Kong's pro-democracy lawmakers have resigned after four of their colleagues were disqualified.
On Wednesday Beijing passed a resolution allowing the city's government to disqualify politicians deemed a threat to national security.
Shortly afterwards the opposition lawmakers said they would leave the city legislature in solidarity.
For the first time since Hong Kong was handed back to China in 1997 the body has almost no dissenting voices.
BBC China correspondent Stephen McDonnell says the legislature was already stacked in favour of the pro-Beijing-camp.
Hong Kong Democratic Party chairman Wu Chi-wai told reporters: "We can no longer tell the world that we still have 'one country, two systems', this declares its official death."
Hong Kong - formerly a British colony - was returned to China under the "one country, two systems" principle, which allowed it to retain more rights and freedoms than the mainland until 2047.
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The dismissal of the four legislators is being seen as the latest attempt by China to restrict Hong Kong's freedoms, something Beijing denies.
China introduced a controversial and far-reaching national security law in Hong Kong in late June, which criminalised "secession, subversion and collusion with foreign forces".
The law was introduced after years of pro-democracy and anti-Beijing protests. It has already led to several arrests of activists and has largely silenced protesters.
The territory's leader, Chief Executive Carrie Lam, is pro-Beijing and is supported by the central government there.
What happened on Wednesday?
The new resolution passed by China's National People's Congress Standing Committee says that lawmakers should be disqualified if they support Hong Kong independence, refuse to acknowledge China's sovereignty, ask foreign forces to interfere in the city's affairs or in other ways threaten national security.
It also allows the Hong Kong government to directly remove lawmakers without having to approach the courts.
Moments after that resolution passed, four lawmakers - Alvin Yeung, Kwok Ka-ki and Dennis Kwok of the Civic Party and Kenneth Leung of the Professionals Guild - were disqualified.
All four of them are considered moderates and they have never supported Hong Kong independence.
The city's pro-democracy legislators have 19 seats in the 70-seat legislature. Within hours of their disqualification, the remaining 15 announced they would resign en masse.
"We... will stand with our colleagues who are disqualified. We will resign en masse," the Democratic Party's Wu Chi-wai said. Their letter of resignation will be submitted on Thursday.
But Chinese foreign ministry spokesman Wang Wenbin said the disqualification of the four lawmakers was "rational, reasonable and in line with the constitution and laws".
"This was a necessary requirement for adhering to and improving on One Country, Two Systems, implementing Hong Kong's Basic Law, as well as Hong Kong's National Security Law," he said at a news conference in Beijing.
The four men were among 12 legislators who were earlier barred from standing in a legislative election planned this year but delayed until 2021.
The group had called on US officials to impose sanctions on those responsible for alleged human rights abuses in Hong Kong.
