Authorities in a north German state have ordered all poultry to be kept indoors after the discovery of bird flu in two farms.

Type H5N8 bird flu was confirmed in a second poultry farm in Schleswig-Holstein on Monday following a case on another farm in the state last week.

A series of outbreaks of the highly pathogenic bird flu have been reported in Europe in past weeks and Dutch health officials on Tuesday ordered the culling of 48,000 chickens following a separate outbreak on a farm.

As of Friday the risk level of avian influenza incursion in wild birds in Great Britain was raised from ‘medium to ‘high’ following two unrelated confirmed cases in England this week and increasing reports of the disease affecting flocks in mainland Europe.

Wild birds are believed to be spreading the disease.

READ MORE: Scotland on 'high' alert over bird flu

The Schleswig-Holstein state agriculture ministry is currently examining the deaths of over 3,000 wild birds there.

On Monday, avian flu ewa discovered in a peregrine falcon in County Limerick, n Ireland’s southwest.

Wild birds impacted in the EU have included Eurasian wigeon, mute swan, greylag goose, cormorant, barnacle goose, curlew, Eurasian buzzard, peregrine falcon, white-tailed eagle, cane goose.

The chief vets from Scotland, England, Wales and Northern Ireland are urging bird keepers to maintain and strengthen their farm biosecurity measures in order to prevent further outbreaks of avian influenza in the UK.

The vets have said the UK has robust biosecurity measures and monitoring in place to prevent the disease spreading in this country and "the risk of transmission of avian influenza viruses to the general public in the UK remains very low".

But the economic cost can be significant.

Health experts say people should avoid touching sick or dead birds, while chicken and eggs are safe to eat if cooked thoroughly, as that kills the virus.

The vets say all bird keepers are being urged to prevent direct or indirect contact with wild birds, with the risk of infection of poultry in Great Britain also being raised from ‘low’ to ‘medium’. Wild birds migrating to the UK from mainland Europe during the winter period can spread the disease to poultry and other captive birds.

A cull of 13,000 birds was ordered at a poultry farm in Frodsham, in Cheshire last week with health officials saying it was the"highly pathogenic strain" related to the virus currently circulating in Europe.

A smaller cull was reported at a farm in Kent, in the south-east of England, where the H5N2 avian influenza strain was detected this week.

All 480 ducks and chickens on the site near the town of Deal were to be killed to limit the spread of the disease, the Government has confirmed.

Schleswig-Holstein’s order to keep poultry indoors would be hard for some farmers but is needed to prevent more farm birds catching the disease, the Schleswig-Holstein state agriculture ministry said in a statement.

The global spread of H5N1 in birds was considered a significant pandemic threat in 2006.

To date, according to the World Health Organisation there have been 455 worldwide deaths due to H5N1.

While prior H5N1 strains had been known, they were significantly different from the 2006 strain on a genetic level, making the global spread of the strain unprecedented.

Concerns famously surfaced in the UK when scientists and vets were conducting urgent tests on a dead swan infected with bird flu that was discovered in Scotland.