Agriculture Minister Julie Collins on Wednesday confirmed the latest case of the H5N1 strain was detected in a migratory bird found in South Australia.
It is the first definite case in the state after two earlier confirmed results in birds that were found on a remote beach in Esperance, about 700km southeast of Perth.
Urgent testing is under way after another suspected case was detected in a seabird found in Quindalup, southwest of Perth.
"This is obviously concerning," Ms Collins said.
"But given the spread of (the virus) globally, it is not unexpected that other migratory birds may have arrived at other locations across the Australian coastline."
A temporary ban on all poultry products imported from Australia, imposed by Papua New Guinea's National Agriculture and Quarantine Inspection Authority, has been lifted after being put in place on Monday.
"We appreciate PNG's willingness to work cooperatively and to remove some of these restrictions," Ms Collins said.
PNG is Australia's largest single market for chicken meat exports, accounting for nearly half of the $133 million in sales in 2023/24.
WA Agricultural Minister Jackie Jarvis said there had been no evidence to date of mass mortalities among birds following the initial discovery of the sick animals.
More than 100 reports of potentially sick birds have been made to the national emergency hotline since the first H5N1 detection.
The poultry and agricultural sectors in Australia remain free from the flu, although the industry has been placed on high alert since the cases were confirmed in wild birds.
Major poultry producer Inghams has since announced it would lock down its WA sites to mitigate against any potential risks.
More than 200 million chickens have been culled in the US since the virus arrived there.
Australia had been the last continent free of the virus strain.
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