A blind Chinese rights activist who made a daring escape from extrajudicial detention was on Friday under the protection of the US embassy in Beijing, according to a friend, as concerns were growing about possible retribution against his family and supporters.

After more than six years of jail and house arrest, Chen Guangcheng was said to have fled under cover of darkness, evading eight checkpoints and close to 100 guards who have been watching his home in the Shandong province countryside.

A photograph released on Friday night shows him with a friend and fellow activist, Hu Jia, who said Chen was under US protection. "It is my understanding that Chen is in the safest place in China. That is the US embassy," said Hu.

If confirmed, the incident could overshadow a planned trip to Beijing next week by the US secretary of state, Hillary Clinton, and treasury secretary, Timothy Geithner.

It would be the second case this year of a high-profile figure seeking refuge at a US diplomatic office in China. In February, Chongqing police chief Wang Lijun fled to the US consulate in Chengdu claiming his life was threatened because of his investigation into the death of British businessman Neil Heywood.

That incident led to a 36-hour standoff during which Chinese security personnel surrounded the consulate until Wang was turned over to an official from Beijing.

The US government neither confirmed nor denied claims that Chen was seeking asylum. An embassy spokesman, Richard Buangan, told reporters that "he did not have any information at this time."The British embassy also said Chen's whereabouts were a mystery. "We have followed Chen Guangcheng's case over a long period of time and have made representations publicly and privately to Chinese authorities. We have seen today's reports and will be following events closely," said a spokesman.The mainstream Chinese media had not reported the escape, but in a video recording apparently made after his release, Chen issued an open call for the prime minister, Wen Jiabao, to investigate his case.

He said between 90 and 100 people were involved in his illegal detention, which included savage beatings that left his wife with broken bones and the harassment of his children. Those who tried to visit him – including lawyers, journalists and the actor Christian Bale – had been either roughed up or driven away.

The accusations throw a harsh light on a Chinese government already reeling from a corruption and wire-tapping scandal sparked by the death of Heywood.

Chen blamed his treatment on local officials and the Chinese state's obsession with maintaining stability at all costs. He said his greatest concern was that the authorities would carry out "insane retribution" on his family, several of whom have already been placed under arrest.

Chen confirmed reports about his maltreatment that have appeared online over the years. "The truth was even worse," he said."

Human rights campaigners expressed delight that Chen – whose case has drawn international attention – was no longer in the hands of the authorities, but concern about revenge attacks on his wife, child, brother and human rights activists who helped him gain liberty.

According to the US-based human rights group China Aid, Chen was "100% safe" in Beijing. But it said the activist He Peirong, one of the people who helped Chen flee, had been arrested at her home in Nanjing on Friday morning.

He, who is said to have been in close contact with the Chen family, had earlier told CNN that Chen's hands were trembling, but his spirits were high. She said he was injured in the escape.

It was not clear how Chen evaded the officials, police and plainclothes thugs who have been camped in and around his home in Linyi since his release from prison in 2010. But activists said it was not an individual, opportunistic bid for freedom.

"To escape from a place with so many guards must have taken a great deal of planning," said Phelim Kine, of Human Rights Watch.

Chen was believed to have used the cover of darkness, in which his blindness – he lost his sight at the age of five – gave him an advantage over his captors. He previously attempted to dig a tunnel.

"I would say the fact that he successfully escaped is a miracle," said Hu. "It's like a real Chinese version of The Shawshank Redemption. I heard he got through eight security checks."

If Chen is caught, he faces the risk of severe extra-legal punishment from his guards. Several people close to Chen have already been rounded up, prompting fears of retribution.

According to the NGO Human Rights in China, Chen's brother Chen Guangfu was taken away from Dongshigu village on Thursday. His nephew, Chen Kegui, was also in hiding after using a kitchen knife to defend his mother from intruders led by the village chief.

Local public-security bureaux were not picking up their phones.

"The wife [Yuan Weijing], children and mother are on the extreme edge of vulnerability," said Kine. "They have already been brutally victimised for merely trying to get outside the compound for food or medical attention, so it is quite likely that the plainclothes thugs will react quite brutally to his escape. It is our hope that all diplomatic missions will make strong representations for their safety."

Chen has suffered the wrath of officials in Shandong since 2005, when he exposed a programme of forced abortions to reach targets linked to China's one-child policy. Although he was released from a four-year jail term in September 2010, he and his family continued to suffer detention and beatings.

Associates say they fear for his health, which has deteriorated during his detention."I don't know if he is safe now and I am worried about him," said lawyer Teng Biao. "Chen was not given freedom after being released from prison and he was sick and did not have a chance to see a proper doctor. I am worried about him."