HANOI, June 18 (Reuters) - Bird flu, which has killed one person since it re-emerged in Vietnam in early May, has flared up on several farms in a northern province despite efforts by the government to stop it from spreading.

The Animal Health Department said on Monday that 690 ducks and chickens died last Thursday and Friday at eight farms in Bac Giang province and officials slaughtered the remaining birds after tests found the dead birds had the H5N1 avian flu virus.

"Bird flu virus is widely present in the environment and has infected many poultry flocks. Therefore, it can happen anywhere now," a government statement quoted Deputy Agriculture Minister Bui Ba Bong as telling a meeting on Saturday.

At the same meeting, Prime Minister Nguyen Tan Dung approved an order to import another batch of 200 million doses of bird flu vaccine to battle the outbreaks that have struck 16 provinces, including Bac Giang, and two cities.

"It is not encouraged to develop the waterfowl flock. Unvaccinated ducks are not allowed to roam on fields and a tight control must be imposed on (the country"e;s) 70 million ducks," the statement quoted Dung as saying at the meeting.

The World Health Organisation (WHO) described the government as "committed and alert" to the dangers of bird flu"e;s spread but that carrying out all effective measures in the provinces was still a challenge.

"There might be a bit of complacency now and that would be of concern," Vietnam representative for the U.N. health agency, Hans Troedsson, said on Monday.

Vietnam"e;s programme of poultry vaccination and other measures has been described by international health experts as a model for keeping the H5N1 virus at bay, but this year it has spread nationwide in ducks and chickens.

Health officials on Saturday confirmed bird flu killed a 20-year-old man on June 10, bringing to five the number of human cases confirmed by Vietnamese officials since May and the first fatality since 2005.

The death raised Vietnam"e;s toll since late 2003 to 43 people.

The WHO has not confirmed the latest cases.

Troedsson said he was "not surprised and it was not unexpected" to see human cases again because "we have to remember the virus never disappeared".

He said none of the five infections, including the death reported by Vietnam"e;s health authorities, had been confirmed by WHO reference labs.

The cases so far were isolated but he said that "if we start to see clusters that would be more of a concern".

Globally, the H5N1 virus has killed 191 people out of 313 known cases, according to a tally by the WHO. Hundreds of millions of birds have died or been slaughtered. (Additional reporting by Grant McCool)