© REUTERSFile photo: Ducks are seen in a field in Bourriot Bergonce, southwestern France.
An outbreak of bird flu has been detected in a duck farm in France's Landes region, the heart of foie gras production, local officials said Sunday.

"Clinical signs leave no doubt and it was decided to cull the flock" on Saturday, the day after the outbreak was identified, Marie-Helene Cazaubon, head of the Landes chamber of agriculture, told AFP.

Local authorities have established a three-kilometer (1.8-mile) protection zone and a 10-kilometre surveillance zone around the farm.

It is the second outbreak detected in the southwest since a major epidemic last year led to the culling of 2.5 million ducks and geese.

Early last month health authorities asked organic and open-air poultry raisers to confine their fowl as a measure to avoid contact with migratory birds that might carry the virus.

"We are in a migratory corridor through which birds fly from northern Europe... and we must be very vigilant," said Cazaubon, herself a duck farmer.

Cazaubon noted that most of the ducks and geese have already been slaughtered for their fatty liver, to be made into the famous foie gras pate popular during the holiday season.

The tradition runs deep in France, but it is controversial because the birds are force-fed in order to fatten their livers artificially.

About one-quarter of French foie gras comes from the Landes, which counts around 800 farms, mainly raising ducks.