HONG KONG (AP) — Hong Kong police arrested 53 former lawmakers and democracy proponents Wednesday for allegedly violating the new national security law by participating in unofficial election primaries for the territory’s legislature last year.

The mass arrests, including of former lawmakers, were the largest move against Hong Kong’s democracy movement since the law was imposed by Beijing last June to quell dissent in the semi-autonomous territory.

“The operation today targets the active elements who are suspected to be involved in the crime of overthrowing, or interfering (and) seriously destroy the Hong Kong government’s legal execution of duties,” said John Lee, Hong Kong’s security minister, in a news conference.

He said those arrested were suspected of trying to paralyze the government, via their plans to gain a majority of the seats in the legislature to create a situation in which the chief executive had to resign and the government would stop functioning.

In a video released by former lawmaker Lam Cheuk-ting on his Facebook page, police turned up at his house and told him he was “suspected of violating the national security law, subverting state power.” Police told those recording the video to stop or risk arrest.

The legislative election that would have followed the unofficial primaries was postponed by a year by Hong Kong Chief Executive Carrie Lam, who cited the public health risks during the coronavirus pandemic. Mass resignations and disqualifications of pro-democracy lawmakers have left the legislature largely a pro-Beijing body.

Lee said the police would not target those who had voted in the unofficial primaries, which were held in July last year and attracted more than 600,000 voters even though pro-Beijing lawmakers and politicians had warned the event could breach the security law.

All of the pro-democracy candidates in the unofficial primaries were arrested, according to tallies of the arrests being reported by the South China Morning Post, online platform Now News and political groups.

At least seven members of Hong Kong’s Democratic Party — the city’s largest opposition party — were arrested, including former party chairman Wu Chi-wai. Former lawmakers Lam, Helena Wong and James To were also arrested, according to a post on the party’s Facebook page.

Benny Tai, a key figure in Hong Kong’s 2014 Occupy Central protests and a former law professor, was also arrested, reports said. Tai was one of the main organizers of the primaries.

The home of Joshua Wong, a prominent pro-democracy activist who is serving a 13 1/2-month prison sentence for organizing and participating in an unauthorized protest last year, was also raided, according to a tweet posted from Wong’s account.

American human rights lawyer John Clancey was also arrested on Wednesday. Clancey was the treasurer of political group Power for Democracy, which was involved in the unofficial primaries.

“We need to work for democracy and human rights in Hong Kong,” Clancey said as he was being led away by police, in a video posted by local online news outlet Citizen News.

Police also went to the headquarters of Stand News, a prominent pro-democracy online news site in Hong Kong, with a court order to hand over documents to assist in an investigation related to the national security law, according to a livestreamed video by Stand News. No arrests were made.

Lee also pointed to a “10 steps to mutual destruction” plan among those arrested, which included taking control of the legislature, mobilizing protests to paralyze society and calling for international sanctions.

That plan was previously outlined by former law professor Tai. He predicted that between 2020 and 2022, there would be 10 steps to mutual destruction which includes the pro-democracy bloc winning a majority in the legislature, intensifying protests, the forced resignation of Chief Executive Carrie Lam due to the budget bill being rejected twice, and international sanctions on the Chinese Communist Party.

The concept of mutual destruction — in which both Hong Kong and China would suffer damages — is popular among some protesters and pro-democracy activists.

“The plot is to create such mutual destruction that if successful … will result in serious damage to society as a whole,” said Lee. “That is why police action today is necessary.”

Senior superintendent Steve Li from the national security unit said in a news conference that 53 people — 45 men and eight women aged between 23 to 64 — were arrested in an operation that involved 1,000 officers.

Six were arrested for subverting state power by organizing the unofficial primaries, while the rest were arrested for allegedly participating in the event, Li said. He said more arrests could be made and investigations were ongoing.

In recent months, Hong Kong has already jailed several pro-democracy activists including Wong and Agnes Chow for their involvement in antigovernment protests, and others have been charged under the national security law including media tycoon and outspoken pro-democracy activist Jimmy Lai.

The security law criminalizes acts of subversion, secession, terrorism and collusion with foreign powers to intervene in the city’s affairs. Serious offenders could face up a maximum punishment of life imprisonment.

Hong Kong leader Carrie Lam had said at the time of the unofficial primaries last year that if their aim was resisting every policy initiative by the Hong Kong government, the election may fall under subverting state power, an offence under the national security law.

Beijing had also called the primaries illegal and a “serious provocation” of Hong Kong’s electoral system.

Following the handover of Hong Kong to China by the British in 1997, the semi-autonomous Chinese city has operated on a “one country, two systems” framework that affords it freedoms not found on the mainland. In recent years, Beijing has asserted more control over the city, drawing criticism that it was breaking its promise of Hong Kong maintaining separate civil rights and political systems for 50 years from the handover.

The sweeping arrests drew condemnation from Anthony Blinken, the U.S. Secretary of State nominee for the upcoming Biden administration, who said on Twitter that it was an “assault on those bravely advocating for universal rights.”

“The Biden-Harris administration will stand with the people of Hong Kong and against Beijing’s crackdown on democracy,” Blinken wrote in his tweet.

Human Rights Watch said the arrests suggest Beijing has failed to learn that repression generates resistance. HRW senior China researcher Maya Wang said in a statement that “millions of Hong Kong people will persist in their struggle for their right to vote and run for office in a democratically elected government.”

In further remarks to The Associated Press, Wang said it wasn’t clear what provisions of the law were being cited to justify the arrests, but that local authorities seem less concerned with legal substance.

“The very nature of the national security law is as a draconian blanket law allowing the government to arrest and potentially imprison people for long terms for exercising their constitutionally protected rights,” Wang said.

“The veneer of rule of law is also applied in mainland China stripped of any meaning. Hong Kong is looking more like mainland China but where one ends and the other begins is hard to discern,” she said.