One of China's best known liberal writers, Bai Hua , has been missing for more than a month. His friends in Shanghai, where Bai is based, have expressed fears that he might have been detained by the authorities. One friend said the playwright and poet had been picked up by public security personnel for a 'lifestyle problem'. He said, however, the real reason for the detention could be the Communist Party leadership's desire to send a warning to avant-garde intellectuals. While Bai, 64, supported the 1989 pro-democracy movement, he has generally kept a low profile. He has published a few books in Taiwan since the early 1990s and has kept up contact with 'bourgeois-liberal intellectuals'. Shanghai authorities were reportedly unhappy with the author's behaviour during a brief trip to the United States last summer to see his son. Bai's wife, Wang Pei, confirmed last night that she had not heard from him since early last month. She said her husband's work unit, the Shanghai branch of the Writers' Association, had been unable to locate his whereabouts. 'I do not know whether his disappearance is a political issue or whether it has to do with his writing,' she said. 'He has not called home since. I am worried but I don't think it is something very serious.' She said her husband left home last month for an undisclosed 'far-off place', but she refused to say what the purpose of the trip might have been. Shanghai police could not be reached for comment last night. Bai was best known for his script for the 1982 film Bitter Love, which infuriated patriarch Deng Xiaoping for its alleged lack of patriotic feeling. Soon afterwards, Mr Deng launched the Campaign Against Spiritual Pollution. Political analysts said while Bai had been careful not to touch politically sensitive topics, Beijing's attitude towards liberal authors had hardened since last winter. They said it was not the first time Shanghai authorities had incriminated liberal intellectuals or cadres. The authorities used the pretext of their pursuing a 'socially unacceptable lifestyle'.