HANOI - VIETNAMESE authorities have found the H5N1 bird flu virus in a batch of chickens smuggled over the border from China, officials said on Tuesday, warning that two northern provinces remained affected.

An official in the border province where the chickens were found did not say how many had been brought in illegally, but state media said eight out of 16 samples taken from the birds carried the virus.

'The samples were taken from chickens smuggled in from China that were confiscated by customs,' the official at the Lang Son Provincial Animal Health Department told Reuters by telephone.

China, home to the world's biggest poultry population with hundreds of millions of farmers raise birds in their backyards, is seen as a crucial front in the global fight against bird flu.

Poultry smuggling is rife along the border between China and Vietnam, even though patrols have been stepped up. Last month the two countries wrapped up drawn out negotiations on demarcating their lengthy and porous border.

Both China and Vietnam have reported in recent weeks outbreaks of bird flu among poultry.

The disease can also infect people, although there have been no cases of human-to-human transmission.

A 19-year-old died in China of the avian flu strain after gutting ducks and in Vietnam an 8-year-old girl was in hospital about 150 kilometres south of Hanoi with the disease after eating poultry that had died. Her 13-year-old sister died this month and a health official said it may have been from bird flu.

Vietnam's agriculture ministry said on Tuesday the bird flu outbreak still affected two northern provinces Thanh Hoa and Thai Nguyen. -- REUTERS