Ducks and geese from a commercial hatchery on the Danish island of Funen are being tested for possible H5 bird flu, the Danish Veterinary and Food Administration said on Thursday.

The farm, which has around 20,000 ducklings and goslings, has been cordoned off while authorities continue tests to discover if the birds are infected with highly pathogenic H5 or a less serious strain of virus.

The infection was discovered through routine tests put in place by the Danish authorities earlier this year.

Three other commercial farms, which have supplied the afflicted farm with hatching eggs, have also been cordoned off.

"The birds at the farm don´t show signs of disease but we also know that ducks can have a serious type of bird flu without showing signs of sickness," Chief Veterinarian Preben Willeberg told Reuters.

The administration expects further test results on Friday.

In May, Denmark halted exports of poultry from Funen after birds on a smallholding farm tested positive for the deadly H5N1 strain of avian flu.

Denmark found its first case of H5N1 in a wild buzzard south of Copenhagen in March. Since then it has tested more than 1,000 wild birds, with at least 40 testing positive for H5N1.