Dutch officials were on Monday checking poultry farms for a highly infectious strain of bird flu following an outbreak in a central village of the virus which could infect humans.
Public health authorities on Sunday banned the transport of poultry nationwide after the discovery in the village of Hekendorp of a "highly pathogenic" form of avian influenza that is very dangerous to birds and can contaminate humans.
British authorities have also reported a bird flu outbreak at a duck breeding farm in northern England but have not specified whether it is the same strain as in the Netherlands.
The destruction of around 150,000 hens at the egg farm in Hekendorp, near Utrecht, should be completed on Monday, said Lex Denden of the Dutch Food and Consumer Product Safety Authority (NVWA).
"We're checking another 16 poultry farms in around a 10-kilometre (six-mile) radius," he told AFP.
"No other cases have so far been detected and we hope to complete the tests today."
- Health risk to humans -
Dutch media reported that the birds would be gassed and that two farms in the immediate vicinity of the infected farm had already been given the all-clear.
Roadblocks have been set up around one kilometre from the village to prevent people not on official business entering.
The atmosphere in the village was quiet on Monday, with police and black barriers screening off the infected farm.
Officials have identified the flu as being the H5N8 strain, previously detected only in Asia, but which was identified on a German farm earlier this month.
Several hundred thousand birds, mainly ducks, have been culled over the last two months because of a South Korean outbreak.
Some strains of avian influenza are fatal for chickens, and poses a health threat to humans, who can fall sick after handling infected poultry.
But Dutch authorities have said human infection can only occur following "intense and direct contact" with infected birds.
Renowned virologist and bird flu expert Ron Fouchier of the Erasmus Medical Center in Rotterdam told AFP it was a mystery how the virus had reached the Netherlands.
"We have no idea where it's coming from," he said, noting that the flu had "popped up, out of nowhere, in farms without any poultry trade record with Asia".
Fouchier said that the infection likely came through wild waterbirds, such as ducks, geese or swans, that had migrated from Asia and left droppings near the Dutch farm.
Fouchier said he did not expect other farms or humans to become infected as outdoor poultry farms had been relocated indoors.
"We can't really talk about a major return of the virus since it's a different strain than in 2005-06," he said.
The H5N1 strain of bird flu has killed more than 400 people, mainly in Southeast Asia, since first appearing in 2003. Another strain of bird flu, H7N9, has claimed more than 170 lives since emerging in 2013.
- Countrywide ban -
The Dutch transport ban is to last a maximum of 72 hours from Sunday and includes moving poultry, eggs and bird manure.
However, in a 10-kilometre ring around the affected farm the ban could last up to 30 days.
Hunting has also been banned for now across the country.
"We are hoping this outbreak will be contained to this farm alone," said Hennie de Haan, incoming chairwoman of the Dutch Poultry Union (NVP), which represents almost half of the country's 2,200 poultry farmers.
"We have learnt a lot since the 2003 outbreak and fortunately protocols have been put in place to deal with this sort of thing," she told AFP.
According to Dutch media, the H7N7 strain of avian flu severely hit the Netherlands in 2003 with health authorities destroying some 30 million birds in an effort to quash an outbreak.
There are some 95 million chickens kept on Dutch poultry farms and egg exports totalled some 10.6 billion euros ($13.2 billion) in 2011, according to the latest Dutch statistics.