Dutch authorities ordered the destruction of 63,000 broiler hens on Tuesday after bird flu was identified at a poultry farm in the northern province of Friesland, the country's fourth outbreak so far this winter.

Bird flu has spread across Europe in recent weeks, forcing some farmers to slaughter flocks or keep them indoors, with the threat taken particularly seriously in the Netherlands, where high farm density can help the virus to propagate.

Authorities also imposed a ban on transporting all poultry materials, including eggs and straw, within a 10 km radius of the farm. Authorities did not say which of several H5 bird flu strains had struck at the farm.

The world's second-largest agricultural exporter, the Netherlands has one of the world's biggest poultry sectors. Almost a quarter of a million birds have been destroyed in the Netherlands during this year's bird flu season.

Nearby France adopted "high risk" measures against bird flu last week after an outbreak of the severe H5N8 virus.