Infection rates are highest among intravenous drug users and sex workers.

In Indonesia, infection rates among blood donors has risen tenfold in the past two years.

But the worst situation is in Cambodia and Burma, where the disease is already well above the UN's epidemic levels of 2%.

Privately, UN officials say that more than 7% of the adult population in Burma are suffering from the disease.

"In some areas", says aids expert Chris Beyrer, "along the borders with Thailand and China, more than 10% of the adult males are HIV positive. This is worse than anything Asia's experienced - and it's an epidemic raging out of control."

Governments must act

The UN says that because of the nature of transmission, through drug users and commercial sex workers, the disease will spread rapidly throughout the population, unless governments recognise the problem and do something to check its spread.

Stephen Kraus is the regional consultant for south-east Asia for UNAids, the UN body that deals with the disease.

He says the first thing governments must do is to accept there is a problem.

"Very few countries have actually done that," says Mr Kraus.

"They insist they don't have a drugs problem and therefore cannot have an Aids problem."

In countries where transmission is largely through sexual contact, like in Thailand and Cambodia, the trend can be halted.

Long term treatment for Aids patients is expensive

A leading UN official in Bangkok, Nanda Krairish, says that with political commitment and the compulsory use of condoms for sex workers the spread of the disease can even be reversed.

"In Thailand, as a result of early prevention programmes and the use of condoms, more than two million Thais are not suffering from HIV who certainly would have if the government hadn't acted as decisively as it did a decade ago."

The World Health Organisation also reports that the tighter control of the commercial sex trade, particularly in the Cambodian capital Phnom Penh, has reduced the estimated incidence of HIV by half in the past year.

Some experts are sceptical about the figures, but agree that the Cambodian Government's intervention will certainly have reduced the spread of the disease.

'Like a bush fire'

The most rapid spread of HIV, say Aids experts, is when the disease originate and spreads through drug users.

"It's like a wild bush fire out of control," says Chris Beyrer. "That's what's happening in northern Burma."

With the size of the populations in Asia, particularly China and India, the problem will be massive.

Peter Piot Executive director of UNAids

UN experts say there is a 50% chance of transmission through joint use of needles by intravenous drug users.

"A drug user who shares needles is certain to contract Aids," says the Director of Asia Harm Reduction, Tom Smits. "Its not a question of if, but when."

The chances of contracting Aids through sexual contact, according to the UN, is only one in a thousand.

The problem though, they say, is when the disease becomes prevalent amongst sex workers.

For years HIV/Aids in Vietnam was restricted to drug users, and the spread of the disease remained relatively constant.

Now many of the country's prostitutes have been infected and there are fears that it will spread much more rapidly.

General population vulnerable

That is the real problem, UN officials say. Although it may start in the vulnerable groups like drug users, sex workers and itinerant workers, it then spreads to the general population.

"Already 40% of the world's HIV sufferers are living in Asia," says Peter Piot, executive director of UNAids.

"And with the size of the populations in Asia, particularly China and India, the problem will be massive."

But the lessons of Asia also offer some hope.

"Thailand's experience can be a model for the future," says Nanda Krairiksh, head of human resources at the UN Economic and Social Commission for Asia and the Pacific.

"It needs political commitment and a multi-sectoral approach; HIV/Aids is not a medical problem, it's a development problem and should be treated as such."

UN officials say if Asian governments adopt comprehensive awareness, early prevention and treatment programmes, including harm reduction policies such as providing drug users with clean needles, a major human tragedy can still be averted.