Britain scrambled to contain its first outbreak of the highly pathogenic H5N1 strain of bird flu in domestic poultry on Saturday after the virus was found at a farm run by Europe's biggest turkey producer.

Some 2,500 turkeys have died since Thursday at the Bernard Matthews farm near Lowestoft in eastern England. The Department for the Environment, Food and Rural Affairs (Defra) said all 159,000 birds there would be culled over the next few days.

"We're in new territory," National Farmers' Union Poultry Board chairman Charles Bourns told Reuters. "We've every confidence in Defra but, until we know how this disease arrived, this is a very apprehensive time for all poultry farmers."

Defra said the virus was the same pathogenic Asian strain found last month in Hungary where an outbreak among geese on a farm prompted the slaughter of thousands of birds.

That outbreak followed a relative lull in cases of H5N1 among European poultry since hundreds of turkeys died at a farm in east France about a year ago.

The strain tends to be transmitted to poultry by infected migrating wildfowl.

It has killed at least 164 people worldwide since 2003, most of them in Asia, and more than 200 million birds have died from it, or been killed to prevent its spread.

But it has not yet fulfilled scientists' worst fears by mutating into a form that could be easily transmitted between humans and possibly cause a global pandemic.

UNUSUAL OUTBREAK

Avian flu expert Colin Butter of the Institute of Animal Health said the British outbreak was surprising as it had happened outside the main bird migration period.

"The next thing we need to know is if this is a primary or secondary case. If this is a secondary case, it is much more serious. If this is the first case, or 'reference case', and we can stamp it out, the outbreak will be controlled," he said.

A protection zone was established with a radius of 3 km (2 miles) and a surveillance zone of 10 km around the infected farm. Bird gatherings such as bird shows and pigeon racing were suspended nationwide.

Across the North Sea, Norway, which has had no cases of the deadly bird flu strain, responded to the news by ordering farmers to keep poultry indoors in the area south of Nordland county and banned bird gatherings, such as bird shows and competitions.

Britain's poultry industry is worth 3.4 billion pounds ($6.7 billion), with 800 million birds produced each year.

The Health Protection Agency said the current level of risk to humans from H5N1 was extremely low.

In May, 50,000 chickens at three farms in Norfolk, also in eastern England and home to some of Europe's biggest poultry farms, were culled after another strain, H7N3, was detected.

A wild swan found dead in Scotland in March had the H5N1 version of the virus. It was thought to have caught the disease elsewhere, died at sea and been washed ashore in Scotland.