Leading Chinese human rights lawyer Mo Shaoping is to defend dissident Huang Qi, accused of "illegal possession of state secrets" after being taken into police custody last week.

Mo, whose past clients include Zhao Yan, a former New York Times staffer who was freed from jail last year after being locked up for fraud, said he had accepted the case on Tuesday.

"Exactly what state secrets he has in his possession is not clear," Mo told AFP on Wednesday.

"I need to find out from Huang Qi and from the police exactly what crime he has committed."

Huang, who has received international awards for his efforts to publicise human rights violations in China, was last seen last week being forced into a car by three men in Chengdu, the capital of southwest China's Sichuan province.

His mother, Pu Wenqing, 74, said he had been in Chengdu to help with quake relief efforts following the 8.0-magnitude earthquake in Sichuan on May 12 that left nearly 87,000 people dead or missing, and millions more homeless.

Mo said he had not yet met with Huang, who was being detained at a police station in Chengdu.

Huang was jailed for subversion from 2000 to 2005 after he set up a website that independently investigated government corruption and advocated democracy.

After being released, he resumed his human rights work and opened the Tianwang Human Rights Centre, which claims to be the only non-government human rights organisation in China.

A lawyer with the rights centre and a professor with a local university who were with Huang when he disappeared, were also taken into custody, according to Pu.