Three of Hong Kong's leading separatists – including leader of the illegal Occupy movement Joshua Wong Chi-fung and founder of a banned separatist party Andy Chan Ho-tin - have been arrested.

Co-founder of Wong's separatist party Demosisto, Agnes Chow Ting, was also arrested on Friday morning at home.

The arrests were made after the Organized Crime and Triad Bureau launched an investigation, said the police.

Wong and Chow, both 22, were arrested for their involvement in besieging the police headquarters in Wan Chai on June 21.

Both are facing charges of inciting others to participate in an unauthorized assembly and participating in an unauthorized assembly. Wong is facing a third charge of organizing an unauthorized assembly.

Demosisto, of which Wong is a leader and Chow a co-founder, said in a social media post that Wong was arrested under three charges around 7:30 am this morning on his way to the South Horizon metro station, in a southern part of Hong Kong. It later stated Chow was also arrested.

On Aug 17, 2017, the High Court sentenced Wong to six months imprisonment for storming the Hong Kong SAR government’s headquarters on Sept 26, 2014. 

On Jan 17, 2018, the court sentenced Wong to three months imprisonment for contempt of court for obstructing a police clearance operation at Mong Kok in Kowloon. The sentence was later reduced to two months after he made an appeal.

In January 2018, Chow was disqualified by the Electoral Affairs Commission of Hong Kong from standing in an election for a seat in the city's legislature, as she was found to have violated the Basic Law.

Chan, 29, was charged with rioting and assaulting a police officer.

Chan, founder of the Hong Kong National Party, a party banned in 2018 under allegations of "Hong Kong independence" advocation, was arrested late Thursday night at the Hong Kong International Airport when he was about to leave for Japan.

On Aug 1, Chan, together with another 10 people in two separate crackdowns, were arrested in Fo Tan, New Territories of Hong Kong, for possessing offensive weapons and explosives without a license.

The case is believed to be connected to the violent protests that have gripped the city since June 9. In this case, he was eventually released on bail and is due to report to the police in September.