Vinod Mishra of the research company Demographic and Health Surveys said Friday the disease has now broken out of the high-risk groups of injecting drug users and sex workers and is spreading through the nation's general population.

``The growing migrant population in China may be the `tipping point' in China's battle with the AIDS epidemic,'' said researchers Xiushi Yang and Valerian Derlega of the Old Dominion University in the United States and Huasong Luo of Yunnan University.

The growth of urban migration in China since the early 1980s has been phenomenal with census data showing a rise of 11 million in 1982 to more than 79 million in 2000 and an estimated 120 million now.

Research by Yang and colleagues found that the risk of HIV infection among temporary urban migrants is much higher than for non-migrants.

They are four times more likely to have unprotected sex and twice as likely to have used illicit drugs in their lifetime. They also found that separation from the social bonds of their village communities is a key factor in migrants' high-risk behavior.

Urban migrants, mostly males in their late teens, live together at their place of work such as construction sites, restaurants and living quarters provided by employers or in camps on the city fringes characterised by poverty, overcrowding and lack of health services.

Mishra said China with 1.3 billion people and India with 1.08 billion are on the frontlines in the battle against AIDS because of their massive populations which means that even small changes in the percentage rate of infection translates into very large numbers of infected people.

``You have to watch the big giants, they will never have the prevalence rates of sub-Saharan Africa, but in terms of the number of people infected they could be huge epidemics,'' Mishra told the conference.

India has 5.1 million people infected with HIV representing 0.9 percent of the population, ranking second behind South Africa with 5.3 million in absolute numbers.