Foreign diplomats and rights groups are closely monitoring the case as concerns mount over the vanishing space for dissent in the former British colony, which has taken a swift authoritarian turn since the imposition of a national security law in June 2020.

Hundreds of people lined up at the court on Thursday to show their support for the defendants, with the hearing due to start at 10am local time.

"The kids wanted to come," said Candy, a 40-year-old housewife who started queuing before 5am with her two children.

"This is a declaration of my support."

The hearings have gone on late into the night for three consecutive days, causing several defendants to fall ill and be sent to the hospital.

A number of the defendants dismissed their legal representatives and plan to add more testimony to their submissions to the court. Hong Kong laws restrict media coverage of the content of bail hearings.

In contrast with the global financial hub's common law traditions, the new security law puts the onus on defendants to prove they will not pose a security threat if released on bail.

The activists, aged 23-64, are accused of organising and participating in an unofficial primary poll last July that authorities said was part of a plan to "overthrow" the government.

The vote, in which not all of the accused were winners, was aimed at selecting the strongest opposition candidates for a legislative council election that the government later postponed, citing the coronavirus.

The detentions have been fiercely criticised by governments in the West, including in Britain and the United States.

Supporters of the security law, which punishes what it broadly defines as secession, subversion, terrorism and collusion with foreign forces with up to life in prison, say it is necessary to restore stability in Hong Kong after months of pro-democracy protests in 2019.

Among those charged were the organiser of the primary election and former law professor Benny Tai, as well as prominent democracy campaigners Lester Shum, Joshua Wong, Owen Chow, Wu Chi-wai and Sam Cheung.

Australian Associated Press