Czech authorities will destroy all 750,000 hens on a poultry farm at the centre of its worst outbreak of avian influenza so far as the disease spread between halls, reported Reuters.

Avian influenza was first detected last week at the farm, located 150 km (90 miles) west from Prague, in one of its three halls, and authorities on Tuesday had begun preparations to cull up to 220,000 birds.

But the Czech Republic's State Veterinary Administration (SVS) said on Wednesday a further spread on the farm had led it to decide to cull all the birds there.

"Despite measures taken and other efforts, it was not possible to prevent the spread of the highly contagious poultry disease to further halls and the whole farm will have to be culled," the SVS said.

The virus can be transmitted to humans in contact with poultry, but experts say the health risk to humans is low.

Czech authorities have required poultry farms to keep flocks indoors since November, but it has seen an uptick in cases in recent weeks.

Avian influenza is pressuring already high food prices and triggering trade restrictions from countries that import poultry.

A record number of chickens, turkeys and other birds have died in outbreaks in the United States and Europe, and the virus is spreading in South America, Africa, and Asia.