HONG KONG — The Hong Kong police arrested dozens of elected pro-democracy officials and activists early Wednesday on suspicion of undermining a new national security law imposed by Beijing after they tried to organize an informal primary election last year for the city’s legislature.
The mass arrests marked the largest roundup yet under the national security law, which the central Chinese government introduced in Hong Kong in June to end months of fierce anti-Beijing protests. The move suggested that the authorities were casting a wide net for anyone who had played a prominent role in opposing the government, even after officials promised that the law would affect only a small number of people.
The Hong Kong police did not immediately identify those arrested, and said an exact count of those detained was not available.
The alleged offenses also underscored government officials’ efforts to weaken any meaningful opposition in the city’s political institutions. Among those arrested were at least six former Legislative Council members, a number of district councilors — a hyperlocal elected position dominated by pro-democracy figures — and several activists. They included figures who had called for aggressive confrontation with the authorities and those who had supported more moderate tactics.
In a Facebook Live video streamed by Ng Kin Wai, a district councilor, as the police arrived at his door, an officer could be heard saying that he was arresting Mr. Ng on suspicion of “subversion of state power.” The officer says he has “reason to believe” that Mr. Ng had participated in the primary in order to win office and ultimately “force Chief Executive Carrie Lam to resign.” (Under Hong Kong law, if lawmakers veto the government budget twice, the leader must step down.)
The Twitter account of Joshua Wong, the former student leader who is one of the most prominent faces of the Hong Kong protests, said that the police had also raided Mr. Wong’s home on Wednesday morning because he had participated in the primary.
Mr. Wong is serving more than a year in jail for his role in a 2019 protest, a charge not linked to the national security law. Convictions under the security law can lead to significantly longer sentences.
According to the social media pages of those arrested or their supporters, at least some of the detainees were accused of subverting state power — an offense under the security law — because they had participated in the informal primary in July. The group had hoped to pare down the number of candidates planning to run in the Legislative Council election in September.
That election was never held because the Hong Kong government postponed it by one year, citing coronavirus concerns. Many democracy supporters accused officials of trying to prevent an embarrassing loss for the pro-Bejing camp. Then, in November, the authorities disqualified four pro-democracy incumbents in the Legislative Council. The remaining opposition members resigned in protest.
More than 600,000 Hong Kongers voted in the unofficial primary election, largely selecting newer candidates who favored a more aggressive approach toward the government, rather than more familiar moderate faces. Some of the activists arrested on Wednesday were among the more outspoken winners, but the police also arrested candidates who had lost their primary races and were less directly involved with the mass protests.
The government has disqualified candidates for what it calls insufficient loyalty, and several of the primary winners were later disqualified from the race before it was postponed. In addition, two top Hong Kong officials, including Mrs. Lam, had warned ahead of the primary that those who participated could be accused of subversion.
Human rights groups condemned the mass arrests. Maya Wang, senior China researcher at Human Rights Watch, said the authorities had removed “the remaining veneer of democracy in the city.”
“Repression generates resistance,” Ms. Wang said in a statement, adding 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.”
Before Wednesday’s arrests, the police had arrested dozens of other people under the national security law, including Jimmy Lai, the media mogul and founder of the pro-democracy newspaper Apple Daily.
Tiffany May and Austin Ramzy contributed reporting.