China's best-known artist Ai Weiwei has been detained at Beijing airport this morning and police have surrounded his studio in the capital.
The 53-year-old, who designed the Olympic Bird's Nest stadium, has been an outspoken critic of the government. Although he has previously experienced harassment by officials, he appeared to be relatively protected by the status of his late father, a renowned poet, and his high international profile; last year, he created the Sunflower Seeds installation for Tate Modern.
His detention comes amid a wider crackdown on activists and dissidents, which human rights campaigners describe as the worst in over a decade. At least 23 people have been detained, mostly in relation to incitement to subversion or creating a disturbance. Three more have been formally arrested and more than a dozen are missing, including high profile human rights lawyers.
Ai was due to fly to Hong Kong for business this morning, but was detained at immigration on his way out of Beijing. An officer told an assistant who was travelling with him that the artist had "other business" and could not board the plane.
Between 15 and 20 uniformed and plain clothes police surrounded his studio in Caochangdi, in the north of the capital, and more were believed to be searching it. Power to the neighbourhood was cut off.
Men who appeared to be plainclothes police grabbed the phone of a Guardian journalist who took a photograph of the scene and deleted the image. A uniformed officer told the reporter: "You are not allowed to be on this street. You must leave."
One resident said: "I went outside to see what was going on and saw a lot of police…I cannot understand it. What has he done?"
Officials visited Ai's studio three times this week, saying they wanted to check that staff there – particularly foreigners – were registered correctly.
But his assistant said Ai appeared to have no particular concerns prior to his detention today.
Ai's mobile was not available and telephones at his studio rang unanswered. Posts about Ai on the popular Weibo microblog were deleted.
Twitter users reported that Ai's friend Wen Tao had been detained by police in Caochangdi. Shortly beforehand, replying to a friend enquiring whether he was all right, he had tweeted: "So far, so good". Wen's mobile was not available.
Beijing police said they did not know anything about either man. Asked about Ai, an airport police spokesman said: "I do not have the obligation to tell you the information. You may have got your information wrong; even if it is right, you have to go through certain procedures to make inquiries, not just make a phone call."
Earlier this week it emerged that Ai was setting up a studio in Berlin because of his increasing work in Europe.
But he told the Guardian that it would take at least two years to build the space and he would probably divide his time between Europe and China.
He said the situation in Beijing was "difficult" and added: "It is hard to know what will happen in a few years.
"I will never leave China behind unless I am forced to….Hopefully that is not going to happen."
Last year Ai was placed under house arrest after saying he would hold a party to mark the forced demolition of his studio in Shanghai.
In December he was prevented from leaving the country. Many dissidents had their movements restricted at the time because of the government's fears that people would attend the Nobel peace prize ceremony for jailed writer Liu Xiaobo.
Ai also complained he was twice assaulted by police in Sichuan, south west China.
Nicholas Bequelin, Asia researcher for Human Rights Watch, said: "This crackdown has not bottomed out yet.
"We are still in this process of weeding out any government critics, with no end in sight."
He added: "Ai Weiwei has been a bit of an outlier and the harassment against him has been more and more intense in the past few months.
"But I think the signal it sends is that if he can be arbitrarily harassed in this way, no one is safe."