Fears are mounting across east and south-east Asia that a flu virus that has killed thousands of chickens could kill humans.

The outbreak, which has affected nearly 600,000 chickens in Vietnam alone, is suspected of having links to the deaths of 10 children and an adult in the Vietnamese capital, Hanoi, the World Health Organisation (WHO) said today.

"There is a possible link," said Peter Horby, a WHO epidemiologist in Hanoi. "In the past, chickens have infected people in outbreaks in Hong Kong in 1997 and again in 2003."

But he added: "Whatever they've got, there doesn't seem to be widespread transmission. It's encouraging that's it's not spreading."

Mr Horby said all the human victims are believed to have come into contact with poultry before falling ill and symptoms appear to be similar in both species.

Vietnam is seeking help from the United Nations to combat the disease.

"We need help from international organisations to effectively put down the bird flu outbreak," Dau Ngoc Hao, deputy director of the Vietnamese agriculture ministry's veterinary department, told Reuters.

The disease has also been detected in Japan, with 6,000 chickens having died in a poultry farm in the town of Ato, Yamaguchi prefecture, around 500 miles south-west of Tokyo, agricultural official Tatsuro Okuhara told Reuters.

Tests have found the bug was a strain of the H5 virus, the same category as the H5N1 disease that spread in South Korea last year, Mr Okuhara said.

Authorities are still investigating whether it is the deadly H5N1-97 strain that killed six people in Hong Kong in 1997.

Eggs that were shipped to market from the Yamaguchi farm have been recalled, and the farm's remaining 28,600 birds will all be destroyed and buried within days, Mr Okuhara added. He said chicken from the farm is not for export.

In Vietnam, officials have been culling birds in the southern Mekong delta provinces of Long An and Tien Giang, where the recent cases have been concentrated.

Last week, 81,000 chickens were buried at a Thai-owned chicken farm in northern Ha Tay province, some 25 miles west of Hanoi.

Samples of the bird flu have been sent to US centres for disease control and prevention, but results are not expected until next week.

About 1.1 million chickens and ducks were culled last month in South Korea after an epidemic of H5N1 there.