Fears that the H5N1 bird flu virus has spread to a second state have been realised, with a third case confirmed in South Australia on Wednesday. 

It comes just days after Australia's first two positive cases of the deadly variant were detected in Western Australia, sending several major poultry producers into voluntary lockdown. 

South Australian Premier Peter Malinauskas said the positive case in his state was found in a Southern Giant Petrel at Knights Beach on the Fleurieu Peninsula. 

He said a local wildlife rescue group had been looking after two sick birds brought to them on June 14, but only one had the virus.  

'Once that was drawn to the attention on June 19 to the relevant authorities in South Australia, we responded quickly and enabled and facilitated active testing of those birds for H5 bird flu,' Malinauskas said.

'This afternoon we received those results and they confirmed that one of those birds was negative and one them was positive. It's important to emphasise that this is a migratory bird.'

He said members of the group who handled the dead bird would receive anti-viral medication if needed. 

A previous outbreak of a different strain of bird flu in early 2025 caused widespread egg shortages in supermarkets, with many chicken farms having to cull birds.

Agriculture Minister Julie Collins said the petrel was a migratory bird and urged people to report any sick or dead birds to authorities. 

'This is obviously concerning but given the spread of H5 globally, it is not unexpected that other migratory birds may have arrived at other locations across the Australian coastline,' she said. 

'We'll continue to work with the states to confirm further test results and to provide updates as results become available.'

There could also be a fourth case nationwide after WA authorities said a third bird in the state returned an initial positive result and is awaiting confirmation from the CSIRO. 

It was found in Dunsborough, about 700km north-west of Esperance, where the first two cases were recorded. 

Collins said she was working closely with her WA and SA counterparts to manage the cases. 

'At this stage there is no evidence of any mass mortalities, there is also currently no evidence of infection in poultry or in our agricultural production system, and there continued to be a low risk to human health,' she said.  

Meanwhile, Aussies have been reassured poultry and egg products are safe to eat and that shortages are not expected.

There has been no evidence indicating the strain has been found in local poultry or agriculture, according Collins. 

'We're not sure yet if it's established in wildlife in Australia,' she told ABC News Breakfast on Tuesday.

But the minister warned lessons from overseas indicate the virus cannot be prevented from spreading, and Australia cannot stop it arriving via migratory birds.

'Experts will decide whether or not it's eradicable or whether or not we manage the disease,' she added.