A leading Chinese human rights activist has been severely beaten in jail by other prisoners on the orders of his guards, Amnesty International has said.
Mr Chen campaigned against official abuses
Chen Guangcheng was reportedly beaten after he insisted on his right to appeal against his sentence and refused to allow his head to be shaved.
The human rights group said it feared for his life and that he was at risk of further torture and ill-treatment.
Mr Chen was jailed in 2006 for damaging property and disrupting traffic.
But his lawyers said the real reason was Mr Chen's exposure of violations of China's one-child policy, including forced sterilisations and abortions.
In a statement, Amnesty said Mr Chen had told his wife that after he refused to have his head shaved, "six other prisoners had pushed him to the floor, encouraged by prison guards, and hit and kicked him hard".
Medical treatment was also withheld from him, the group said.
"He has since begun a hunger strike in protest, refusing water as well as food," it added.
"He said he was being punished for 'being disobedient' due to his insistence on filing an appeal to the provincial higher court."
Amnesty said Mr Chen, who is blind, required either the assistance of his lawyer or his wife to help him draft an appeal, but that the prison authorities had refused to let them visit him for longer than 30 minutes per month.
He lost an earlier appeal against his four-year sentence in January.
The London-based group said Mr Chen was a "prisoner of conscience, jailed solely for his peaceful defence of human rights".
"The Chinese authorities must stop the persecution of people who stand up for human rights; as the Olympic Games draw closer, the world will be watching to see whether human rights promises have been honoured. At present they have not," it said.
Mr Chen, 35, has campaigned against what he says are abuses of the Chinese government's one-child policy.
Before being imprisoned, he accused local health workers in Linyi city, in Shandong province, of illegally forcing hundreds of people to have late-term abortions or sterilisations.
China brought in its one-child policy 27 years ago, in a drive to curb population growth, but forced sterilisation and abortion are prohibited.