Human rights monitoring groups say a Chinese court has sentenced three pro-democracy activists to as many as five years in prison on charges of inciting the overthrow of the communist government.

The groups say the Guangzhou Intermediate People's Court in the southern city of Guangzhou on Friday gave the heaviest sentence to lawyer Tang Jingling following a closed-door trial.

Activists Wang Qingying and Yuan Xinting were sentenced to two-and-a half and three-and-a half years, respectively.

The three were taken into custody in May 2014 amid a sweeping crackdown on dissident surrounding the 25th anniversary of the June 4, 1989, pro-democracy protests centered on Beijing's Tiananmen Square.

Tang's wife, Wang Yanfang, has said her husband downloaded Internet writings on non-violent resistance and distributed copies.

Calls to the court rang unanswered.