A China court's sentencing of 10 democracy activists to up to three years in jail has come under fire from rights groups Thursday.

The activists were jailed Wednesday months after they were apprehended by mainland coast guards fleeing to Taiwan from prosecution for riot charges in Hong Kong.

"These sentences meted out after an unfair trial lay bare the dangers faced by anybody who finds themselves tried under the Chinese criminal system," Amnesty International Asia regional director Yamini Mishra said in a statement Thursday.

The Shenzhen's Yantian District People's Court sentenced 31-year-old Tang Kai-yin and 33-year-old Quinn Moon to three years and to years' jail time, respectively, for their role in the illegal border crossing by speedboat.

The others were sentenced to "lighter punishment" of seven months in prison for participating in the illegal crossing, according to a statement released by mainland authorities.

Two minors, aged 16 and 17 at the time of their arrest in August, were returned to Hong Kong.

The case drew international attention and concern after details of their treatment by the mainland justice system was publicized by family members and lawyers in Hong Kong.

"We are deeply concerned that members of the Shenzhen 12 were tried in secret, having been given just three days' notice of their trial," UK Foreign Secretary Dominic Raab said in a statement Dec. 28.

Their trial was closed. Foreign diplomats tried to attend but were refused entry, according to Raab.

The accused were denied visits by family and were not given a choice of legal representation and those with health problems weren't allowed treatment.

 "We urge Chinese authorities to conduct trials in accordance with due process and judicial transparency in line with international Human Rights norms and standards," a Canada foreign ministry representative said.