HONG KONG (AP) — Hong Kong's pro-democracy lawmakers announced Wednesday they would resign en masse after four of them were ousted from the semiautonomous Chinese territory's Legislature in a move one legislator said could sound the "death knell" for democracy there.

The resignation of the 15 remaining pro-democracy lawmakers will ratchet up tensions over the future of Hong Kong, a former British colony that has long been a regional financial hub and bastion of Western-style civil liberties but over which China's government has increasingly tightened its control. A new national security law imposed by Beijing this year has alarmed the international community.

The mass departure will also leave Hong Kong's Legislature with only pro-Beijing lawmakers, who already made up a majority but can now pass bills favored by Beijing without much opposition.

The lawmakers told a news conference they would submit their letters of resignation on Thursday. The announcement came hours after the Hong Kong government said it was disqualifying the four legislators — Alvin Yeung, Dennis Kwok, Kwok Ka-ki and Kenneth Leung.

The ousters came after China's National People's Congress Standing Committee passed a resolution this week saying that any lawmaker who supports Hong Kong's independence, refuses to acknowledge China's sovereignty over the city, threatens national security, or asks external forces to interfere in the city's affairs should be disqualified.

"Today we will resign from our positions because our partners, our colleagues have been disqualified by the central government's ruthless move," Wu Chi-wai, the leader of the pro-democracy camp, told reporters.

During the news conference, the lawmakers held hands and chanted, "Hong Kong add oil! Together we stand!" The phrase "add oil" is a direct translation of a Chinese expression of encouragement.

"This is an actual act by Beijing ... to sound the death knell of Hong Kong's democracy fight because they would think that, from now on, anyone they found to be politically incorrect or unpatriotic or are simply not likable to look at, they could just oust you using any means," lawmaker Claudia Mo told reporters.

In recent months, Beijing has increasingly clamped down on Hong Kong, which it took back control of in 1997, despite promising at the time to leave the territory's more open legal and economic systems intact for 50 years until 2047.

Beijing imposed a national security law in June that some have labeled draconian after anti-government protests rocked the city for months last year, and it has used it to crackdown on opposition voices.

In response, the U.S. leveled sanctions on several officials, including Hong Kong's pro-Beijing leader, several Western countries have suspended their extradition treaties with the territory, and Australia and Britain offered Hong Kongers easier paths to settle in those countries.

Britain said Wednesday that the decision to remove the lawmakers raises further concerns.

"This campaign to harass, stifle and disqualify democratic opposition tarnishes China's international reputation and undermines Hong Kong's long-term stability," Foreign Secretary Dominic Raab said in a statement.

Beijing has rejected the criticism and lashed out at what it calls gross foreign interference in Chinese politics.

On Wednesday, Hong Kong's leader, Carrie Lam, defended the lawmakers' removal, telling reporters that legislators must act properly and that the city needs a body comprised of patriots.

"We cannot allow members of the Legislative Council who have been judged in accordance with the law to be unable to fulfill the requirements and prerequisites for serving on the Legislative Council to continue to operate in the Legislative Council," Lam said.

Still, Lam said that the Legislature would not become a rubber-stamp body, and that diverse opinion is welcome.

"In terms of legality and constitutionality, obviously, from our point of view, this is clearly in breach of the Basic Law and our rights to participate in public affairs, and a failure to observe due process," Kwok, one of the ousted lawmakers, told reporters, referring to Hong Kong's mini-constitution.

Earlier in the year, the four lawmakers were barred from seeking reelection in a vote originally scheduled for September — but remained in their posts. They were disqualified over their calls for foreign governments to impose sanctions on Hong Kong and Beijing.

The government eventually postponed the planned September election by a year, citing the coronavirus, but the pro-democracy camp criticized the move as an attempt to block them from taking a majority of seats in the Legislature — which was a possibility in the coming election.

Chinese Foreign Ministry spokesperson Wang Wenbin said that the disqualification was necessary to maintain rule of law and constitutional order in Hong Kong.

"We firmly support the (Hong Kong) government in performing its duties in accordance with the Standing Committee's decision," Wang said at a regular news conference Wednesday.