The World Organization for Animal Health (OIE) says six European countries have so far been hit by an outbreak of avian flu, an infectious bird disease which could threaten poultry there.
The OIE said on Thursday that a severe strain of avian flu was reported in Germany, Switzerland, Poland, Austria, Hungary and Croatia.
Official veterinary reports posted on the OIE website showed the H5N8 virus was found this week in the northern German state of Schleswig-Holstein on 58 tufted ducks, a great black-backed gull and a coot.
A similar outbreak in Switzerland occurred in ducks.
Meanwhile, Poland and Austria reported cases of avian flu in several types of wild birds.
Poland also reported an outbreak of H5N8 in ducks and a gull near the German border, while Croatia said it had found the virus in swans in the eastern part of the country.
Hungary discovered the disease in a swan near the Serbian border, the reports said.
The Dutch government said on Wednesday it had ordered farmers in the Netherlands to keep poultry flocks indoors after suspected infections of the highly pathogenic H5N8 virus had been found in several countries.
Wild migrating birds can transmit bird flu to farmed poultry.
The H5N8 virus is highly contagious in birds; however, it has never been found in humans.
In 2014, the virus led to massive poultry culling in the EU.