China’s crackdown in Hong Kong escalated dramatically on Wednesday with police arresting as many as 50 opposition figures in their largest operation since a draconian security law was imposed on the financial hub.

The sweep is the latest salvo in Beijing’s battle to stamp out opposition in the semi-autonomous business hub after millions hit the streets in 2019 with huge and sometimes violent democracy protests.

Two senior police sources who both requested anonymity told AFP “around 50” had been arrested by the city’s new national security unit on Wednesday morning.

A tally of arrest announcements made by opposition figures and parties on Facebook and Twitter confirmed at least 48 arrests, most on a charge of “subversion”.

The detentions sparked a rebuke from Antony Blinken, US President-elect Joe Biden’s pick for Secretary of State, who decried the police action as “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,” he added.

Those detained represented a broad cross-section of Hong Kong’s opposition, from veteran former pro-democracy lawmakers such as James To, Andrew Wan, Lam Cheuk-ting and Claudia Mo to a host of younger activists.

Among the youth campaigners were Gwyneth Ho, a former journalist turned social activist, district councillor Tiffany Yuen and Jeffrey Andrews, a campaigner known for working with ethnic minorities.

Colleagues of Joshua Wong, one of the city’s most famous democracy activists who is currently in jail, said via his official Facebook account that his home was searched.

– ‘Night of the long knives’ –

National security police also searched a law firm known for taking on human rights cases. John Clancey, an American lawyer working for the firm was arrested on suspicion of subversion, two sources told AFP.

It is the first time a US national has been detained under the new law.

The police operation also involved the media.

Three local news outlets — Stand News, Apple Daily and Inmediahk said national security police visited to request documents.

“This is a real night of the long knives, the largest single attack upon democracy in Hong Kong yet,” Antony Dapiran, a lawyer who has written books on the city’s protest movement, wrote on Twitter.

Nathan Law, a prominent democracy leader who fled overseas last year, accused authorities of trying to “extinguish the flames of resistance” with the latest arrests.

Hong Kong police did not respond to requests for comment on how many had been arrested and why.

But opposition figures said the arrests were linked to a primary organised by pro-democracy parties last year ahead of local legislative elections which were ultimately scrapped altogether.

More than 600,000 Hong Kongers turned out to vote in the unofficial primary, which was aimed at picking who would stand for election in Hong Kong’s legislature — a body where only half the 70 seats are popularly elected.

The aim of the campaign was to win all 35 elected seats and take a majority in the legislature for the first time to stymie government policies.

At the time, Beijing officials had warned that campaigning to win a majority constituted “subversion” under the new security law.

– New security powers –

The national security law was imposed on Hong Kong in late June in response to the 2019 protests, targeting acts Beijing deems to be secession, subversion, terrorism and collusion with foreign forces.

Officials said the security law would only target an “extreme minority”.

But it swiftly silenced dissent and outlawed a host of peaceful political views with dozens of prominent figures targeted even before Wednesday’s operation.

Over the course of the last year, prominent democracy supporters have been arrested, jailed, barred from politics or have fled overseas.

National security crimes carry a maximum of life in prison and bail is not usually granted for those who are charged.

The law also toppled the legal firewall between Hong Kong’s independent judiciary and the mainland’s Communist Party-controlled courts.

China has claimed jurisdiction over especially serious security crimes and has allowed its security agents to operate openly in the city for the first time.