The fate of millions of migrant workers in Asia hangs in the balance as the deadly SARS virus spreads, governments impose harsh new travel restrictions and shaky economies nose-dive, a top UN official said on Friday.

Dealt a body blow by the Severe Acute Respiratory Syndrome virus, the economies of several countries in the region are forecast to shrink in the second quarter, potentially drying up demand for Asia's mobile workforce.

"If SARS hangs around for a while, the more significant impact than travel restrictions on migrant workers may turn out to be on the demand side," Jerrold Huguet, the top demographer at the UN Economic and Social Commission for Asia and the Pacific, told Reuters in an interview.

"The impact could be devastating."

More than five million foreign workers, from Filipina maids to Indonesian labourers and Vietnamese plantation workers, oil the wheels of commerce in the region, sending home in excess of $20 billion each year to their families.

Studies show most of those families used the remittances for consumption -- buying cars and building new houses -- directly improving standards of living and boosting their local economies.

Among the throng of migrating labourers, an estimated 210,000 Thais left home to work abroad in 2000, as did 416,424 Indians, 376,000 Indonesians, 841,000 Filipinos and 31,000 Vietnamese, according to the most recent United Nations data.

Rethink needed

Many of the countries and territories they head for, including Singapore and Hong Kong, are among the hardest hit by SARS, which has killed more than 260 people worldwide and infected some 4,600 since it emerged in China late last year.

In Singapore, foreign workers make up 24 per cent of the labour force. Seven per cent of workers in Hong Kong are foreign.

Huguet said other countries, such as Japan, which has yet to report a significant SARS toll, are also at risk as a result of those foreign workers.

"China doesn't take in many foreign workers, but quite large numbers of Chinese go abroad, essentially illegally, to Japan and Taiwan. With the smuggling of Chinese workers into these countries, there is huge potential for spreading the disease."

"Japan has some 600,000 foreign workers," he said, noting that figure did not include illegal labour.

Huguet said that while SARS so far appeared to be mainly spread by business travellers and holiday-makers, taking a huge toll on the airline and leisure industries, governments also needed to rethink the way they handled migrant workers to prevent them from succumbing to the disease and accelerating its spread.

"A lot of clandestine migrants or irregular migrants have difficulty in getting health services, like the Indonesians in Malaysia or the Burmese in Thailand," Huguet said.

Governments needed to acknowledge that illegal migrant groups exist and reach out to them with information and health care, or would face potentially devastating consequences.