China's best-known artist, Ai Weiwei, has been detained in Beijing and police have searched his studio, confiscated computers and questioned assistants.

The 53-year-old remains uncontactable more than 12 hours after officials held him at the capital's airport.

Ai, who designed the Olympic Bird's Nest stadium, has been an outspoken critic of the government.

Although he has repeatedly experienced harassment, he appeared to be relatively protected by the status of his late father, a renowned poet, and his international profile. Last year, he created the Sunflower Seeds installation for Tate Modern.

His detention comes amid what human rights campaigners have described as the harshest crackdown on activists and dissidents in over a decade.

At least 23 people have been criminally 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.

Officials detained Ai at immigration control as he attempted to catch a flight to Hong Kong for business. An officer told an assistant travelling with him that the artist had "other business" and could not board the plane.

Uniformed and plainclothes police surrounded and searched his studio in Caochangdi, in the north of the capital. Power to the neighbourhood was cut off.

Men who appeared to be plainclothes officers grabbed the phone of a Guardian journalist who photographed the scene and deleted the image. A uniformed man said: "You are not allowed to be on this street. You must leave."

A staff member told the BBC Chinese news service that officers had taken away eight of Ai's assistants and volunteers.

A friend of the artist tweeted that most had been released but that his wife Lu Qing and two employees remained out of contact.

Police are thought to have searched two other properties relating to Ai and visited the mother of his two-year-old son.

Twitter users reported that police also detained Ai's friend Wen Tao. 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."

Lawyer Liu Xiaoyuan, who has acted for Ai on several occasions, spent several hours at a police station. It was not clear if it was related to the artist's case.

Officials visited his studio three times this week, saying they wanted to check that staff there were registered correctly.

Ai's assistant said, however that the artist 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.

Earlier this week it emerged that Ai was setting up a studio in Berlin. 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 announcing a party to mark the forced demolition of his studio in Shanghai.

In December he was prevented from leaving the country, amid government fears that people would attend the Nobel peace prize ceremony for the jailed writer Liu Xiaobo.

Ai also complained he was twice assaulted by police in Sichuan, in the south west.

In an interview recorded on Friday, he told German TV station ARD: "There are two surveillance cameras at my gate entrance, my phone is tapped, and every message I send on my microblog is censored by them. Obviously, I am not free."

Crackdown on dissent

Ai Weiwei has long been a thorn in the Chinese government's side, but human rights campaigners see his detention as part of the wider crackdown that has seen activists, dissidents and lawyers detained or go missing.

"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," said Nicholas Bequelin, Asia researcher for Human Rights Watch. "I think the signal it sends is that if he can be arbitrarily harassed in this way, no one is safe."

The drive by security officials follows anonymous calls for "jasmine revolution" protests, echoing the uprisings in the Middle East. Although the posting was on an overseas website, and there was little sign of domestic support for the appeal, officials began detaining and harassing people within hours of its appearance.

In part, they seem to be investigating who is behind the appeal. But Patrick Poon, executive secretary of the China Human Rights Lawyers Concern Group, said he believed the calls were being used as an excuse to crack down on high profile human rights defenders. Many believe authorities are seeking to roll back the increased space that critics have carved out for dissent in the last decade. They also suggest the drive reflects the growing strength of the security apparatus.

"The possible impact on China's image is apparently not an issue for them, because that has nothing to do with stability, and stability is the first priority," said Joshua Rosenzweig of the Dui Hua foundation, which supports political prisoners.