Wong -- who is currently behind bars -- was arrested on a new charge of subversion, the first time he has been detained under the new national security law.

The 24-year-old is one of the city's most recognisable democracy advocates and is currently serving a jail sentence for his role in organising democracy protests.

More than 1,000 police officers detained 53 prominent figures -- including a US citizen -- in dawn raids Wednesday on charges of "subversion", a new national security crime that carries up to life in prison.

Local media reported Tam Tak-chi, another activist currently in custody on a sedition charge, was also arrested for subversion on Thursday morning.

Meanwhile, western nations have accused Beijing of using its crackdown to shred the freedoms that were promised under the "One Country, Two Systems" setup when the British colony was returned to China.

"The United States will not stand idly by while the people of Hong Kong suffer under Communist oppression," US Secretary of State Mike Pompeo said in a late-night statement after a day of political violence in Washington.

"The United States will consider sanctions and other restrictions on any and all individuals and entities involved in executing this assault on the Hong Kong people," he added.

Washington has already sanctioned multiple Chinese and Hong Kong officials, including city leader Carrie Lam.

British foreign minister Dominic Raab called the detentions "a grievous attack on Hong Kong's rights and freedoms" and said Beijing "deliberately misled the world about the true purpose" of the security law.

Canada, France and the European Union also issued statements condemning sliding freedoms in Hong Kong and called for the release of those detained.

The alleged offence of those arrested for subversion was to organise an unofficial primary last summer to decide who would stand as candidates for the city's partially-elected legislature in the hopes they might take a majority for the first time.

Many of those candidates were ultimately disqualified from standing and authorities scrapped the election because of the coronavirus.

The sweep was the latest salvo in Beijing's battle to stamp out dissent in the semi-autonomous city after millions hit the streets in 2019 with huge and sometimes violent democracy protests.

Those detained are 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.

John Clancey, an American national and long term Hong Kong resident who worked at a prominent human rights law firm, was also arrested for subversion.

Hong Kong police can hold anyone arrested for up to 48 hours before they must be presented in court.

Those charged with national security crimes are not usually granted bail.

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.