Ai Weiwei has been detained by Chinese authorities with no explanation. Though he was arrested with a number of his colleagues and his studio was raided, all the others have been released. Ai remains in custody, his whereabouts unknown:

Jennifer Ng, an assistant who accompanied Mr. Ai on Sunday morning, said he was taken away by uniformed officers as the two of them passed through customs at Beijing International Airport. Ms. Ng said she was told to board the plane alone because Mr. Ai “had other business” to attend to. She said Mr. Ai was planning to spend a day in Hong Kong before flying to Taiwan for a meeting about a possible exhibition. […]

Shortly after Mr. Ai was seized, more than a dozen police officers raided the artist’s studio in the Caochangdi neighborhood, cut off power to part of that area and led away nearly a dozen employees, a mix of Chinese citizens and foreigners who are part of Mr. Ai’s large staff. By Sunday evening, the foreigners and several of the Chinese had been released after being questioned, according to one of Mr. Ai’s employees, who was not in the studio when the public security agents arrived.

China Takes Dissident Artist Into Custody (New York Times)