A Chinese court has sentenced a man who posted pro-democracy articles online to eight years in jail, his lawyer said Thursday, as China cracks down on dissent ahead of a leadership transition.

Cao Haibo was sentenced for "subversion of state power" by a court in the southwestern city of Kunming, his lawyer Ma Xiaopeng told AFP.

The 27-year-old had worked in an Internet cafe and advocated constitutional democracy online, setting-up web chat groups for discussion of social issues, US-based advocacy group Human Rights in China said in a statement.

The court claimed the case involved state secrets and did not hold an open trial, said the group citing Cao's wife.

Ma said the court put forward evidence that Cao "created an online discussion group, and published articles on foreign websites".

The verdict reflects efforts by the ruling Communist Party to clamp down on dissent ahead of a once-in-a-decade handover of power scheduled to take place at a party congress later this month.

Prominent dissidents have been placed under house arrest before the transition, rights groups said, while more than a million "volunteers" have been employed to keep order on Beijing's streets, according to state media.

In February a court sentenced democracy activist Zhu Yufu to seven years in prison for posting a poem calling for a Chinese-equivalent of the Arab Spring.

Subversion charges are often used to jail government critics. Nobel Peace Prize winner Liu Xiaobo was convicted on the same charge in 2009 and sentenced to 11 years in prison.

A spokeswoman for the Kunming Intermediate Court refused to comment on the case. Ma said he was not sure whether his client would appeal the verdict.