An outbreak of bird flu has likely killed about 3,000 seals off the coast of Sweden and Denmark this year, Swedish authorities announced Tuesday, raising the alarm a month after Germany.

"So far this year about 3,000 harbour seals have died in Swedish and Danish waters and were probably infected with the bird flu virus H10N7," the Swedish Agency for Marine and Water Management said in a statement.

The virus was first detected among sick and dead seals found in April off the coast of Gothenburg southwest of Sweden -- and the agency said the death toll was far higher than initially thought.

In October the numbers of seals killed by the virus was estimated at about 700 but researchers now say most of the dead animals had sunk, making estimates difficult.

"We still don't have the full picture of how many seals are affected or exactly how the infection has spread," a biologist at the marine agency said.

The agency believes that most Swedish seals have probably been infected with the virus but that the majority have developed antibodies which protect them.

Sweden has an estimated 10,000 seals.

In late November, authorities in the northern German region of Schleswig-Holstein reported that 1,600 seals had died from the bird flu virus out of a population of 13,000.

There have also been some reports of seal deaths related to bird flu in Norway and the Netherlands.

German cull ordered after H5N8 bird flu confirmed
Berlin (AFP) Dec 16, 2014 - German authorities on Tuesday ordered the cull of thousands of farm animals after a bird flu outbreak was confirmed as the highly pathogenic H5N8 strain.

The precautionary move came after the discovery at a poultry farm in a rural region of Lower Saxony state.

Regional agricultural minister Christian Meyer said that 19,000 animals at the site and another 12,000 turkeys at a neighbouring farm would be slaughtered.

He said the strain detected in the Cloppenburg district was the same as that found at another farm in November in Schleswig-Holstein state.

Meyer expressed concern that the virus could spread quickly.

"Cloppenburg is a traditional heartland of the poultry industry," he said.

The district had already imposed a three-day ban on all poultry transports to thwart the potential spread of H5N8.

Some strains of avian influenza are fatal for birds, and pose a health threat to humans, who can fall sick after handling infected poultry.