Two teenage pro-democracy campaigners among a group of 12 Hong Kong activists held in China will be sent back to the city on Wednesday, police said.

The "Hong Kong 12" were arrested by the Chinese coastguard on August 23 as they allegedly tried to escape the city by speedboat for sanctuary in Taiwan.

Wednesday's handover comes as verdicts for the other 10 were expected to be handed down by a court in the southern city of Shenzhen on charges of illegally crossing the border or arranging for others to do so.

The two teens, aged 16 and 17, were expected to be handed back by Shenzhen authorities to the city's police force at the border around noon (0400 GMT).

The Hong Kong pro-democracy activists went on trial on Monday
The Hong Kong pro-democracy activists went on trial on Monday AFP / Noel Celis

The Yantian District People's Procuratorate in Shenzhen said that it would not pursue its case against the two teenagers, surnamed Hoang and Liu, who it said had admitted wrongdoing.

The "Save HK12" campaign group said the families had yet to be informed about the handover.

Eight of the 10 adults are accused of illegally crossing the border, while the remaining two are suspected of arranging for others to do so.

The 10 appeared before the Yantian District People's Court on Monday, but the trial -- like many in China's opaque legal system -- was not open to foreign reporters or diplomats.

Families of the accused were only notified of the trial date three days before the hearing, while their lawyers have been barred from meeting the detainees.