A Chinese court on Wednesday jailed 10 Hong Kong democracy activists for up to three years over a bid by the group to flee the city by speedboat to seek sanctuary in Taiwan.

The group were arrested by the Chinese coastguard on August 23 en route to the self-ruled island, which has opened its doors to Hongkongers amid a growing crackdown on dissent in Hong Kong.

The Shenzhen Yantian District People's court sentenced Tang Kai-yin to three years in jail and Quinn Moon to two years for organising an illegal border crossing.

The eight others were sentenced to seven months behind bars for illegally crossing the border.

Officials earlier said that two minors from the so-called "Hong Kong 12" would be returned to Hong Kong after they admitted wrongdoing.

The pair arrived back in the city around noon on Wednesday.

The 10 adults in the group first appeared before a court in the southern city of Shenzhen on Monday, but the trial -- like many in China's opaque legal system -- was not open to foreign reporters or diplomats.

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

These 10 were also fined up to 20,000 yuan (US$3,060) in addition to their jail terms.

But the Yantian District People's Procuratorate said it would not pursue its case against the two teenagers, surnamed Hoang and Liu.

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

The lawyers on Wednesday said the sentences were too heavy and the allegation of organising a border crossing was not substantiated.

The United States on Monday called for the immediate release of the group who it said were "fleeing tyranny".

"Communist China will stop at nothing to prevent its people from seeking freedom elsewhere," a US embassy spokesperson told AFP.

Some of the group were already facing prosecution in Hong Kong, where democracy activists last year led massive protests against Beijing's rule that have since been stamped out by a tough new security law.

China