A long-nosed fur seal has died from H5 bird flu in South Australia, marking the first confirmed case in a mammal on the Australian mainland.

The seal was found dead at Beachport on Wednesday on the state’s Limestone Coast.

It marks a fresh escalation in the spread of the virus days after the South Australian premier, Peter Malinauskas, announced three mass mortality events on offshore islands involving more than 1,000 greater crested terns.

The highly pathogenic strain of bird flu has killed millions of birds globally and crossed over into mammal species, including elephant seals.

Long-nosed fur seals and the endangered Australian sea lion are among the mammal species the federal government has assessed as facing very high risk from the virus.

The SA government has also confirmed a little penguin found at Kangaroo Island this week also tested positive for H5 bird flu.

More to come.