All Hong Kong's pro-democracy lawmakers have resigned after Beijing forced the removal of four of their colleagues, reports BBC.
On Wednesday Beijing passed a resolution allowing the city's government to dismiss 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.
The dismissal of the four legislators is viewed by many 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.
Hong Kong Democratic Party chairman Wu Chi-wai told reporters following the lawmakers' removal: "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.
UK Foreign Secretary Dominic Raab has called the Chinese resolution "a further assault on Hong Kong's high degree of autonomy and freedoms under the UK-China Joint Declaration".
"This campaign to harass, stifle and disqualify democratic opposition tarnishes China's international reputation and undermines Hong Kong's long-term stability."
Human rights organisation Amnesty International has also condemned the move. "Bulldozing through arbitrary decisions via the Chinese government makes a mockery of the rule of law," Asia-Pacific regional director Yamini Mishra said.
The territory's leader, Chief Executive Carrie Lam, is pro-Beijing and is supported by the central government there.