A highly infectious form of bird flu has been confirmed for the first time in Antarctic seals, threatening one of the most fragile ecosystems on the planet.

Scientists working for the UK's Animal Plant Health Agency (APHA) detected the variant of the H5N1 virus in samples taken from dead elephant and fur seals on the sub-Antarctic island of South Georgia.

Dozens of animals are known to have died, with many more likely to have succumbed in remote bays and out at sea.

Experts at British Antarctic Survey told Sky News that the unfolding tragedy was a "mass mortality event".

Dr Marco Falchieri, from the APHA, spent three weeks collecting samples from wildlife on South Georgia, a UK Overseas Territory in the Southern Ocean.

He said seals and seabirds share the same beaches, giving the virus a chance to transmit.

"It is significant because this level of mortality is not normally seen in this population," he said.

"The fact that we found the virus suggests that it is responsible for the casualties that have been seen."

Virus has swept the globe

The 2.3.4.4b form of the virus has swept the globe, spread by migrating birds. It has caused mass die-offs in several seabird colonies in the UK.

Any movement of the virus between birds and mammals is a concern to scientists who closely monitor 'spillover events' for any sign that it is mutating.

It's thought to have killed thousands of sealions around South America, as well as large numbers of mink and foxes being farmed for fur in Europe. It has been detected in a small number of mammals in the UK, including seals and wild foxes.

But there's no good evidence that the virus is spreading between mammals and the APHA scientists found no indication that the virus had adapted to surviving in seals.

These animals share the same environment with birds," said Dr Falchieri.