HONG KONG — Dozens of Hong Kong opposition figures, including an American lawyer, were detained on subversion charges Wednesday in what activists see as a brazen attempt to clamp down on any remaining dissent in the semi-autonomous Chinese territory.

Hong Kong police confirmed to ABC News that around 1,000 officers were deployed Wednesday to arrest 53 people for an alleged act of subversion, searching 72 locations.

Steve Li Kwai-Wah, senior superintendent of the Hong Kong Police Force’s national security unit, said six individuals were arrested for organizing the alleged act, while the other 47 were arrested for participating. Police also froze 1.6 million Hong Kong dollars ($206,000) in funds. Li said the group tried to use strategic voting to secure more than 35 seats in the Hong Kong Legislative Council, with the aim of vetoing the government’s budget, forcing the city’s leader to resign and shut down the government.

The wave of arrests marks the most significant roundup of pro-democracy figures under a controversial national security law, since China imposed the legislation in Hong Kong six months ago.

Most of the detainees were either running in or organizing an unofficial primary in July last year to select opposition candidates for September’s legislative election, which the Hong Kong government later announced it would postpone by a year due to the coronavirus pandemic. Many were popular district councilors who swept the election in November 2019, as the city was in the throes of anti-government protests.

At the time of the July poll, Hong Kong Chief Executive Carrie Lam had warned that it could constitute an act of subversion.

American human rights lawyer John Clancey was among those arrested Wednesday, making him the first known U.S. citizen to be detained under the Hong Kong national security law. Clancey works for the Hong Kong law firm Ho, Tse, Wai & Partners, which was seen in video circulated on social media being raided by police during Wednesday’s crackdown.

Clancey is also chairman of the Asian Human Rights Commission and treasurer of Power for Democracy, which was one of the organizers behind the unofficial July 2020 primary.

Dozens of those arrested updated their Facebook pages to confirm they had been detained on suspicion of “subversion of state,” including Claudia Mo, Leung Kwok-hung and Eddie Chu, as well as co-organizer of the unofficial primary, Benny Tai. Colleagues of prominent activist Joshua Wong, who co-founded the now-disbanded pro-democracy group Demosisto in 2016, said that his home was also searched on Wednesday.

One of the lesser-known detainees is Lee-Chi-yung, who was standing in last year’s election to make the city more accessible for wheelchair users. Lee was motivated by his late daughter’s struggle with a severe disability.

Under the Hong Kong national security law, which criminalizes anything the Chinese government regards as subervsion, secession, terrorism or colluding with foreign forces, those arrested could receive a maximum sentence of life in prison.

Ronny Tong, a senior advisor to Lam, Hong Kong’s leader, told ABC News he is confident that due process will be upheld.

“I understand a lot of people are very concerned about certain pan democrats being arrested by the SAR government in relation to a so-called primary” Tong said. “I have every confidence that, while it seems a lot of people are being arrested, they will be treated fairly, according to the law.”

Prominent Hong Kong activist Nathan Law, who fled to London shortly before the national security law came into effect, called the mass arrests “outrageous.” Law was another founding member of Demosisto, which was disbanded the same day Beijing imposed the new legislation.

“It’s a blatant act of disregarding people’s democratic right and an insult to democracy,” he told ABC News. “This is another round of political persecution. I urge the international community to react, including the European Parliament to halt the EU-China investment deal.”

Emily Lau, a former Democratic Party lawmaker who was the first woman to be directly elected to the Hong Kong Legislative Council in 1991, also weighed in on the latest detentions, calling them “disgraceful and ridiculous.”

“This is a blatant attempt to intimidate pro-democracy activists and warn people not to engage in politics and collaboration,” Lau told ABC News.

U.S. President-elect Joe Biden’s pick for secretary of state, Antony Blinken, took to Twitter to condemn the Hong Kong arrests, calling them “an assault on those bravely advocating for universal rights.” He said Biden’s incoming administration “will stand with the people of Hong Kong and against Beijing’s crackdown on democracy.”

The timing of the detentions has raised some eyebrows, occurring amid a crucial U.S. Senate runoff election in the battleground state of Georgia and just two weeks before Biden’s inauguration.

“It seems like quite an aggressive move and it is not going to sit well in Washington,” said David Zweig, professor emeritus of social science at the Hong Kong University of Science and Technology and managing director of Transnational China Consulting Limited.

“One would think that they may have waited to do something like this until the new administration is in,” he told ABC News. “Maybe people think that now is the chance, now that there is a break between the election and the inauguration and that this gives them time to do this.”

The arrests also come a week after the European Union agreed to a trade deal with China, which has been seven years in the making.

Wednesday’s detentions are part of a broader crackdown on the pro-democracy movement that gripped Hong Kong for months in 2019, mounting one of the biggest challenges to China’s Communist Party rule in decades. Protests have more or less died down since the national security law came into effect.

Beijing says the legislation is necessary to restore stability in Hong Kong. But the law has come under intense criticism from the international community, with both the United States and the European Union saying it stifles freedoms meant to be guaranteed under the “one country, two systems” arrangement between Hong Kong and the Chinese mainland.

Other prominent opposition activists who remain detained under the national security law include media tycoon Jimmy Lai and Agnes Chow, who co-founded the now-disbanded Demosisto group along with Wong and Law.