A former Chinese health official has disappeared and an Aids conference has been cancelled in a suspected police crackdown on unofficial efforts to publicise the illness.

Wan Yanhai, 43, director of the Aizhi Aids advocacy group, which includes the British Embassy in Beijing among its sponsors, has not been seen since Friday. He was taken away by four police officers who burst into his Beijing offices.

His disappearance came a day before the rights advocate Chen Guangcheng, who documented cases of forced abortions in northeastern China, was to appear in court for a second time. A witness who said that he had been coerced to testify against Mr Chen, who is blind, in the first trial was taken away by police yesterday.

The Blood Safety, Aids and Legal Human Rights Workshop, due to start yesterday, was part of activities to mark World Aids Day on December 1. China has one of the fastest-growing rates of HIV/Aids infection, but its communist rulers are anxious to retain control of information about the spread of the condition and feel threatened by an increase in the number of non-governmental organisations (NGOs) attempting to create awareness about its causes and dangers.

Beijing is extremely nervous about any organisation that works outside the remit of the Communist Party and has taken action over the past 12 months to try to regulate NGOs and halt the rapid growth in non-official groups dedicated to battling such problems as health and pollution.

The Health Ministry said last week that 183,733 people were confirmed with HIV/Aids at the end of October, a 27.5 percent rise in the number of official reported cases compared with the end of last year.

However, Aids activists and UN health officials say that the real number of sufferers is probably significantly higher but many people are either too ignorant about the illness, or too afraid of the social stigma, to seek treatment.

The workshop organised by Mr Wan was due to be attended by about 50 people who had contracted Aids, or HIV, which causes Aids, from unsafe blood transfusions, often administered by local government-related medical institutions. While the majority of China’s HIV carriers are believed to be linked to high-risk groups such as intravenous drug users and sex workers, an increasing number have contracted the illness through tainted blood.

In the late 1990s several villages in central Henan province were devastated by Aids after farmers contracted it as a result of selling their blood in government-backed blood drives. The blood buyers paid the donors for plasma, separated the red blood cells and then reinfused the farmers with pooled cells. The pooled cells were contaminated with HIV and as many as 250,000 people became infected.

Mr Wan’s Aids Action Group works to assist the victims, despite a series of obstacles put up by the local and central governments. He spent nearly a month in jail in 2002 after being accused of sending abroad official documents linked to the Henan Aids scandal.

Mr Wan was dismissed from his post in Beijing’s public health bureau in 1994 after being rebuked for his fight against the epidemic and for supporting equal rights for homosexuals.

China's crisis

69,000 blood donors and recipients infected with HIV/Aids

Times Recommends

• Would you live on the wrong side of the Berlin Wall?
• Wish you were here, says Iraq tourist board
• Russian policeman’s corruption plea to Putin