Two minors in the group have been returned to Hong Kong, reports BBC.

These 12 people were arrested in August after they were attempting to escape after a harsh new security law was introduced by Beijing in June.

The Shenzhen Yantian District People's court sentenced Tang Kai-yin, 31, and Quinn Moon, 33, to three years and two years in jail, respectively, for organising an illegal border crossing, a statement was quoted as saying by BBC.

The remaining eight activists were sentenced to a "lighter punishment" of seven months in prison for illegally crossing the border, it added.

Responding to China’s sentencing of 10 Hong Kong residents who have been detained in mainland China since attempting to leave Hong Kong by speedboat in August, Amnesty International’s Asia-Pacific Regional Director Yamini Mishra said: "These sentences meted out after an unfair trial lay bare the dangers faced by anybody who finds themselves tried under the Chinese criminal system. This group of young Hongkongers will be at risk of torture and other ill-treatment in Chinese jails."

“The Chinese authorities have shown the world once again that political activists will not receive a fair trial. Diplomats, journalists and family members were not allowed to observe the effectively closed-door hearing on Monday," Mishra said.

“The Hong Kong youths were deprived of the right to defend themselves through legal representation of their own choosing. Multiple mainland lawyers attempted to represent them at the families’ request, but they have been threatened by the Chinese authorities to force them to drop the cases," Mishra said.