Leading Chinese dissident Li Wangyang, jailed for more than 22 years after the 1989 Tiananmen democracy protests, died in strange circumstances in central China Wednesday, his family and rights groups said.

Li, 62, was found dead in a ward at Daxiang hospital in Shaoyang city, Hunan province Wednesday morning, his brother-in-law Zhao Baozhu told AFP by telephone.

Police appeared to suspect suicide as the cause of death and had taken Li's body away without the family's permission, Zhao said.

"Last evening we were together, Li Wangyang did not show any signs of suicide, it is strange," Zhao said.

"Li Wangyang is a man with a strong mind and strong spirit. Police have taken away his body without the approval of the family."

Zhao refused to comment further, saying he feared his phone was being monitored by police.

Officials at the hospital when contacted by AFP said the cause of death was unclear.

As a leading dissident Li was subjected to heavy police surveillance with up to 10 guards monitoring his hospital ward, rights groups said.

Li had met supporters ahead of the 23rd anniversary of the Tiananmen democracy protests, brutally crushed when soldiers fired upon unarmed students and citizens in central Beijing on June 3-4, leaving hundreds, if not thousands, dead.

The Hong Kong-based Information Centre for Human Rights and Democracy in China said Li was found by his sister and brother-in-law hanging from a window in his ward by a bandage tied around his neck.

"We cannot rule out that security guards monitoring him tortured him to death and faked a suicide," the centre said in a statement.

Once a factory worker in Shaoyang, Li was sentenced to 13 years in prison for "counter-revolutionary" crimes for his role in the 1989 Tiananmen protests, which spread nationwide, the centre said.

Not long after his release in 2001, he was arrested and convicted of "inciting subversion" and sentenced to another 10 years.

According to the Chinese Human Rights Defenders, mistreatment in prison left Li nearly deaf and blind and he had trouble walking.

"Li's sudden death leaves one shocked and suspicious," the group said in a statement.

"He did not commit suicide after over 22 years of bitter, bitter treatment in prison, so why would he commit suicide after gaining his freedom?"