The mother of Mr Ai, Gao Ying, told RTHK that the family had been trying to contact the police to find out the whereabouts of her son. She said her daughter-in-law had written several letters to various government departments but there has been no reply.

Some mainland media reported that the Public Security Bureau had tried to contact the family through different channels. The mother said that was untrue.

The government has said that Mr Ai was under investigation for economic crimes.

State media has accused Mr Ai of plagiarism and described him as a "third-rate" artist who only protested to seek attention.