Beijing has remoulded Hong Kong in its authoritarian image after huge and sometimes violent pro-democracy protests in 2019, imposing a security law that criminalised subversion, secession, terrorism and foreign collusion.

The international non-governmental organisation closed its two offices in Hong Kong in 2021, saying at the time that the security law "made it effectively impossible" for rights groups to work freely.

Amnesty's secretary general Agnes Callamard said on Tuesday that its new section "demonstrates the resilience of our movement, our determination never to be silenced, and our commitment to defending human rights no matter the challenges we face".

The branch, which is officially registered in Switzerland, said it is the first to be "founded and operated entirely 'in exile'" and will be led by Hong Kong diaspora activists in Australia, Canada, Taiwan, Britain and the United States.

Fernando Cheung, a former Hong Kong lawmaker who joined as a board member, said top priorities include raising awareness on "prisoners of conscience" and transnational repression.

"It is clear that Hong Kong's human rights situation has continued to worsen," said Cheung, citing the jailing of a social worker last week over a police-protester clash in 2019.

"Being abroad, we have more latitude to speak up and connect with other international groups, as well as to conduct research and respond to events," he added.

As of this month, Hong Kong has arrested 322 people and convicted 163 of them under two security laws -- one imposed by Beijing, and a homegrown one enacted last year.

Police have also issued bounties on 19 overseas pro-democracy activists.

One of the named activists, Joey Siu, said she hoped the Amnesty office can "encourage Hong Kongers living in the city or abroad in a difficult time", adding that it was a "gesture of courage in response to repression".