According to the public service company RTHK, among those arrested are three well-known leaders of the democracy movement in Hong Kong, James To, Lam Cheuk-Ting and Lester Shum.
According to pro-democracy data on Facebook, quoted by the news agency Reuters, they are said to have been arrested for being on the ballot papers for the election in Hong Kong which was supposed to be held in September last year, but which was postponed with reference to the corona pandemic.
Support from China
About 1,000 police officers took part in the operation.
The arrests took place at dawn with the support of the National Security Act introduced last year, which many observers have described as the nail in the coffin of the doctrine "One country, two systems", which guaranteed the region's residents certain democratic freedoms and rights since the 1997 handover.
The democracy movement has been under increasing pressure since the law came into force.
Maya Wang, of Chinese Human Rights Watch (HRW), told Reuters that the Chinese authorities "remove the last traces of democracy in the city" and continue:
"Beijing once again shows that its leaders have not learned from their past mistakes in Hong Kong: that oppression is generating resistance and that millions of people in Hong Kong will persevere in the struggle for the right to vote and stand for election to democratically elected governments."
Employees of Joshua Wong, who was sentenced to prison in December for his role in an illegal demonstration last year, state that police also entered his home.
A hell
The Chinese Foreign Ministry expresses its support for the Hong Kong authorities, while Taiwanese rulers are shocked by the action.
The Taipei government writes in a statement that Hong Kong has gone from being "the pearl of the Orient" to "the purgatory of the Orient".
US President-elect Joe Biden's incumbent Secretary of State Antony Blinken wrote on social media that "the widespread arrests of pro-democracy protesters are an attack on those fighting for universal rights", and that the incoming US government is behind Hong Kong's struggle for democracy.