Chow was one of the best known young faces of the 2012, 2014 and 2019 protest movements against Beijing's increasingly authoritarian rule in Hong Kong.

She spent around seven months behind bars for her role in a protest outside the city's police headquarters in 2019, when huge crowds rallied week after week in the most serious challenge to China's rule since Hong Kong's 1997 handover.

On Sunday -- Chow's 27th birthday -- she published two posts breaking the silence she had kept since she was released more than two and half years ago.

"I don't want to be forced to do anything any more, and I don't want to be forced to go to mainland China any more," she said.

She said her decision came after "considering the situation in Hong Kong, my personal safety, my physical and mental health".

She announced that she left for Toronto in mid-September for university studies and she would not return to Hong Kong in December to report to the police as her bail conditions demand.

Chow was one of nine people arrested in 2020 alongside pro-democracy media tycoon Jimmy Lai accused of "colluding with foreign forces to endanger national security".

She was released on police bail on conditions including surrendering her passport and reporting regularly to police.

However, in early July, Hong Kong police offered to return her passport on the condition that Chow would travel with them once to the mainland Chinese city of Shenzhen.

She agreed, and in mid-August spent a day with five police officers, where she was shown an exhibition of China's achievements and the headquarters of tech giant Tencent -- where she was requested to pose for photos.

"I could feel that I had been watched throughout the whole trip," Chow wrote.

A Beijing-imposed national security law has criminalised much dissent and most of the city's democracy leaders have been arrested, jailed or fled overseas.

Chow's fellow activist leader Joshua Wong was jailed in Hong Kong over a "subversion" case while Nathan Law has fled abroad with a HK$1 million bounty over his head.

AFP has reached out to Hong Kong police for comment.