The Nobel-winning democracy activist imprisoned by China after leading a call for democratic reforms has been released to a hospital for treatment of late-stage liver cancer.

Liu Xiaobo's incarceration focused global attention on Beijing's harsh treatment of those willing to challenge the Communist Party. Jailed 11 years for subversion in 2009, he was behind bars when he was awarded the Nobel Peace Prize in 2010, his absence starkly marked with an empty chair on stage.

On Monday, his lawyer, Mo Shaoping, confirmed that Mr. Liu was granted medical parole after being diagnosed with cancer. It's unclear what his medical prognosis is. Mr. Mo has not been allowed to meet his client, who is among China's highest-profile political prisoners.

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Globe editorial: Nobel Peace Prize shows China still an outlier on human rights

"About 10 days ago, when his family visited him, they said his illness was still stable," he said in an interview.

A former professor who was banned from the classroom, Mr. Liu spent decades speaking out against China's authoritarian one-party rule. He was imprisoned after participating in the protests that led to the 1989 massacre of students around Tiananmen Square, and later sent for three years to a re-education-through-labour camp.

But he continued to speak critically on some of China's most sensitive topics and, in 2008, co-authored Charter 08, a lengthy document that decried the "disastrous" modernization of China under the Communist Party, which "stripped people of their rights, destroyed their dignity, and corrupted normal human intercourse."

Mr. Liu was jailed the following year, and many signatories to the document – a list that grew to include thousands – have either been detained or barred from speaking to media.

"I am very worried" about Mr. Liu's illness, said He Weifang, a law professor and Charter 08 signatory. Reached by telephone, he could say no more. "I am unable to speak of late. I'm sorry," he said.

Despite the domestic restrictions, Mr. Liu has occupied a central spot in the narrative of China's struggles to win global favour despite commanding a domestic regime whose governing practices many of its trading partners have criticized.

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Beijing froze diplomatic ties with Norway shortly after Mr. Liu was made a Nobel laureate, and sought to exact economic revenge on the Scandinavian country. And the rising clout of the world's second-largest country has made it increasingly risky for other Western countries to anger Beijing.

Late last year, Norway and China normalized diplomatic relations after Oslo pledged that it "attaches high importance to China's core interests and major concerns, will not support actions that undermine them, and will do its best to avoid any future damage to the bilateral relations."

In giving Mr. Liu his award, the chairman of the Nobel peace prize committee had compared him with South Africa's Nelson Mandela and archbishop Desmond Tutu, and Aung San Suu Kyi, the Myanmar democracy advocate who is now de facto ruler of her country. He received the award for "long and non-violent struggle for fundamental human rights in China."

Charter 08 called for the establishment of constitutional rule, protection of human rights, entrenchment of broad civic freedoms and creation of a democratic system that would enable "government truly 'of the people, by the people, and for the people.'"

The Chinese activist "represented the hope that China could go in a more peaceful democratic political direction," said William Nee, China researcher at Amnesty International. By jailing him, the "Chinese government sent a hardline signal that they wouldn't allow that type of activism."

It's a trend that has grown more pronounced under President Xi Jinping, whose administration has led campaigns against human-rights lawyers, labour activists and civil-society groups.

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Mr. Liu's wife, Liu Xia, has also been kept under house arrest since 2010. Two years later, she wept in a brief interview with The Associated Press, saying her treatment has been "absurd and unbelievable." She has been deprived of communication and forced to live with police officers.

Mr. Nee called Mr. Liu's illness "obviously a tragic case. The government needs to do everything possible to ensure that more tragedy doesn't occur by ensuring that he gets adequate medical care, releasing him and ensuring that Liu Xia is finally able to visit him and meet with him without restrictions."

Other prominent Chinese activists similarly face health problems they fear have been exacerbated by their detention and the quality of medical care they are allowed to receive.

Dissident Hu Jia, whom Chinese authorities keep under strict surveillance, suffers cirrhosis of the liver and this year was diagnosed with acute pancreatitis that may mean surgery later this summer. The revelation of Mr. Liu's cancer, he said, should focus "more attention on the health condition of fighters like us, whether we are in prison or under house arrest."

Heavy censorship has kept many in China from following Mr. Liu's case. On Monday, searches of his name on local social media returned no Chinese language results. But one person managed to sneak through a message in English, using his initials: "Blessing for Dr. LXB, who is the Nobel Peace Price winner and famous prisoner of conscience, best wishes to him! Justice will prevail over evil."