BEIJING: Chinese authorities said Wednesday they were starting the prosecution of 12 Hong Kong activists who were caught while allegedly trying to flee the city for Taiwan by boat.

The group was snared some 70 kilometres (43 miles) southeast of the city on August 23, authorities said previously, before being handed to police in the neighbouring mainland metropolis of Shenzhen.

In a social media notice, the People's Procuratorate of Yantian District in Shenzhen said Tang Kai-yin and Quinn Moon were suspected of organising for others to cross the border.

Eight others, including Cheng Tsz-ho and Cheung Chun-fu, stand accused of an illegal border crossing.

Two others involved in the case, who are minors, face non-public hearings, according to the notice.

The activists -- whose arrests were formally approved in September -- had disappeared into China's opaque judicial system since their capture, with lawyers struggling to access them and family members expressing fear over their fate.

Some of those aboard the boat were facing prosecution in Hong Kong for activities linked to last year's huge and often violent pro-democracy protests.

Although Hong Kong has its own internationally respected common law legal system, where detainees are promptly produced after their arrest and tried in open court, mainland China's judicial system is notoriously opaque, with conviction all but guaranteed.

In June, Beijing imposed a new security law on Hong Kong, announcing it would have jurisdiction for some crimes and that mainland security agents could openly operate in the city.

With Beijing clamping down on Hong Kong's democracy movement, democratic Taiwan emerged as a sanctuary, quietly turning a blind eye to residents turning up without proper visas or paperwork.