A further 220,000 chickens have been killed after an outbreak of bird flu at factory farms in Noord-Brabant and in Noord-Holland.

All birds on the three farms have been killed as a precaution and the situation on eight other nearby farms is being monitored closely, officials said.

The new culls take the total number of birds killed since the epidemic started to over 1.2 million. The current epidemic of bird flu is the worst ever to hit Europe, according to the German authorities. So far the virus has been identified on 18 Dutch factory farms.

The Dutch outbreak started at an organic poultry farm in Zeeland in October last year and was preceded by reports of a rise in dead wild birds. Outgoing agriculture minister Carola Schouten then initiated national measures to prevent the disease from spreading and all poultry are now required to be kept indoors.

There are also tough restrictions on the movement of birds and how to deal with their manure.