Mr. Liu, 61, has said he wanted to be treated abroad, but his lawyer said the authorities would not allow it. Doctors from the United States and Germany visited Mr. Liu on Saturday and said then that he could be moved, but his condition has apparently worsened.

He is experiencing septic shock and blood clotting, the hospital said.

“The patient’s condition is life threatening, and the hospital is doing everything it can to save him,” the statement said. “Family members already know the situation.”

Mr. Liu was a university lecturer and literary critic in Beijing who became a prominent figure in the 1989 Tiananmen protest movement. He organized a hunger strike in the final days of the protest, and he helped students retreat from Tiananmen Square as the military moved in. He was imprisoned afterward, the first of multiple prison terms.

In 2008 he was arrested for spearheading Charter 08, a pro-democracy manifesto that called for an end to authoritarian rule in China. It was signed by hundreds of scholars and activists, a number that has since grown into the thousands.

When he was convicted of inciting subversion in 2009, Mr. Liu told the court that he hoped he would be “the last victim of China’s endless literary inquisitions and that from now on no one will be incriminated because of speech.”