Earlier, outgoing US ambassador Jon Huntsman had raised the artist's case in a strongly worded speech in Shanghai, describing him as one of the activists who "challenge the Chinese government to serve the public in all cases and at all times".The artist's detention has sparked an international outcry, with the US, Britain and the European Union criticising a crackdown on dissidents and activists. Germany's foreign minister, Guido Westerwelle, has summoned the Chinese ambassador over the issue.
Police visited Ai's studio three times in the week before he went missing. "He felt a premonition that he would be detained," his wife Lu Qing told AP. "He told me something might happen to him."
She said she was particularly worried about his health as he takes medication for several illnesses.
While Ai had repeatedly clashed with authorities, friends had already warned that this case appeared more serious because police had removed dozens of computers and documents from his studio and had questioned his assistants.
Earlier in the day, Ai's mother, Gao Ying, told Reuters: "I think they detained him for a reason. If they think they have something, it's certainly a fixed case, an injustice. I think they'll concoct some things against him."
Gao said she had been "filled with a bit of dread" since Ai angered authorities by listing the names of children who died when schools collapsed in the 2008 Sichuan earthquake. Officials censored discussion of the subject after public anger developed over shoddy construction.
On the Sina microblog, China's domestic equivalent of Twitter, censors deleted many messages about Ai, and a search for his name produced a warning that results were not shown due to local regulations. But internet users fought back with typical ingenuity. Several used the words "ai weilai" or "love the future" – which looks and sounds similar to his name – to call for his return. One wrote: "I really don't dare believe that in this society, even love for the future can disappear."