China could have 10 million people infected with HIV by 2010 - possibly the highest number of any country - if preventive measures were not adopted now, the mainland's leading expert on the disease warned yesterday. 'HIV has spread from China's borders to inland areas and from metropolitan to rural areas,' Professor Zeng Yi, president of the Beijing-based Chinese Foundation for Prevention of STD and Aids, told the opening of the Hong Kong Aids Conference. 'It is critical to take action now, otherwise this window of opportunity to control the Aids epidemic in China will be lost.' If action was not taken, the mainland would become 'the country with the largest number of HIV cases in the world', he said. His warning was the strongest statement yet by a mainland official about the extent of the Aids crisis and followed an acknowledgment last week by Vice-Minister of Health Yin Dakui that the country was facing a 'very serious epidemic of HIV/Aids'. The Health Ministry and the World Health Organisation had previously predicted there would be 600,000 mainland people with HIV by the end of last year. Officials estimate that 20 to 70 per cent of the mainland's 860,000 drug-users have HIV, while 30,000 to 50,000 people have been infected by tainted blood. Professor Zeng said the epidemic, which had entered 'a rapid increasing phase', would have an impact on Hong Kong's HIV situation. 'Because of close contact between Hong Kong and the mainland, I think the situation in China is very important to Aids across the border in Hong Kong,' he said later. 'We cannot stop sexual contact and we should tell people to have safe sex.' His concerns were echoed by another keynote speaker, Dr Helene Gayle, director of the United States' National Centre for HIV, STD and TB Prevention, part of the Centres for Disease Control and Prevention. 'This [figure of 10 million] is very possible because of the large population. There is a real fear that just very small increments in prevalence could mean . . . millions of people being affected,' she said. 'What happens in China is going to affect Hong Kong.' Dr Gayle will head to Beijing today to meet Ministry of Health officials to discuss a collaboration between the US and the mainland to stem the rise. Professor Zeng said the central Government's target of containing HIV infections to 1.5 million by 2010 was 'very difficult to reach'. He said sex would become the main route of HIV transmission, pointing to a 30 per cent rise in sexually transmitted diseases each year, to an estimated six million to eight million cases last year, and a rise in the number of sex workers to about 600,000. But Dr Gilles Poumeral, the Aids regional adviser at the World Health Organisation's Western Pacific Region, said it would be difficult to project how the mainland HIV epidemic would develop. 'Whether it will be 10 million or 20 million in 10 years we do not know. There is risk behaviour for HIV transmission in China and there are obvious concerns that HIV will expand if no appropriate interventions are made,' he said from Manila. India has 3.7 million HIV cases, making it the largest in Asia and the second in the world, after South Africa, with 4.7 million cases, according to UN figures.