A Chinese human rights lawyer whose secret detention and alleged torture by Communist authorities prompted an international outcry has been released after a three-year jail sentence, his wife and a relative said.

Gao Zhisheng, who defended some of China's most vulnerable people including Christians and coal miners, has been held largely incommunicado since 2009.

"He is out [of jail], but he has not returned home - he's at his father-in-law's house in Urumqi," a close relative of Gao told AFP by telephone, referring to the capital of the far-western region of Xinjiang where the lawyer had been serving his sentence.

The relative added that Gao's health was "normal, quite good", but asked not to be named because of the sensitivity of the matter.

It was not clear whether Gao, 50, will still be subject to some form of house arrest as he has been previously.

His wife Geng He, who now lives in the United States, told AFP she had spoken to Gao following his release but was worried that he had been "tortured" in jail.

"Five of his upper teeth are very loose, and three lower ones are bad, my sister said he has to break bread into little pieces before he can eat it."

Beijing-based activist Hu Jia said a relative of Gao told him the lawyer would stay in Urumqi to receive treatment because his "teeth are in a bad condition" before returning to his hometown in the northern province of Shaanxi.

Gao was convicted of "subversion of state power" in 2006, and given a suspended sentence of three years in prison. He was immediately placed under house arrest and put on probation for five years.

In 2009 he was detained by Chinese security officers and held in secret for more than a year, with his family not told of his whereabouts.

After returning home for a month in March 2010, he went missing again. State media said in 2011 that he had been sent back to jail for three years after a Beijing court said he had violated his probation terms.

The decision was criticised by the United Nations, the United States and the European Union, which repeatedly called for Gao's release, and by rights groups such as Amnesty International.