Bird flu has hit another province in northern Vietnam despite government efforts to halt its spread, the Agriculture Ministry said on Monday.

Tests on ducks and chicken at a poultry farm in Bac Ninh province, just 30 (20 miles) northeast of Hanoi, showed they were infected with the H5N1 virus, the ministry’s Animal Health Department said.

All 950 birds on the firm were slaughtered immediately on May 25, it said.

The latest outbreak took to 10 the number of cities and provinces struck by the H5N1 virus in less than a month, the department said.

Many of the provinces which have detected the infection this month are along the national north-south Highway One, suggesting poultry movement should be tightened further to keep the virus from spreading, officials said.

The Animal Health Department said 36 provinces had completed the first phase of poultry vaccinations against bird flu.

The Agriculture Ministry said it held a national conference of animal health officials on Monday to discuss measures to stop the outbreak from spreading, including a second campaign to vaccinate poultry against the deadly virus.

International public health officials describe Vietnam’s mass poultry vaccination programme and other measures as a model for keeping the virus at bay for the past 18 months.

But last Wednesday it recorded the first human case since November 2005 when a man from Vinh Phuc province, near Hanoi, was found to have contracted H5N1 after he helped slaughter chickens at a friend’s wedding about a month ago.

The World Health Organisation said it was working with the government to investigate the case and needed to verify the virus sample. It said finding the suspected patient was not alarming if it was an isolated case.

The H5N1 virus has killed 42 people in Vietnam since it re-surfaced in Asia in late 2003.

The virus returned to poultry in the south late last year. Last month, WHO urged Vietnam to accelerate poultry vaccination and target more ducks, which can carry the virus without showing symptoms.

Vietnam has vaccinated more than 121 million poultry in 63 of its 64 provinces so far this year, the Animal Health Department said.

The spread of the virus in May, at the beginning of summer, is unusual as experts say it appears to thrive best in cool temperatures and weakens in warmer weather.