Three seabirds with deadly H5N1 were detected earlier this week, two in Western Australia and one in SA.
Australia's Chief Veterinary Officer Beth Cookson said on Saturday WA had reported a further detection in a giant petrel on the state's southern coast.
WA has also reported a further suspect bird, with a giant petrel found at Roses Beach, west of Esperance, on June 21.
That bird was found among four others, with samples sent for confirmatory testing at the CSIRO's centre for disease preparedness.
The other birds found at Roses Beach had thankfully returned negative results, WA Agriculture Minister Jackie Jarvis told reporters on Friday.
"At this stage, there have only been detections in vagrant migratory seabirds that occasionally visit southern Australia," Dr Cookson said.
"There remains no evidence of any mass mortality events and there are no detections in poultry or in our agricultural production system.
"The risk to human health remains low."
WA authorities had by Friday received some 360 reports of sick birds since the first suspected case was found on a remote beach in Esperance, about 700km southeast of Perth.
About 43 have been prioritised for further investigation and testing, with 12 returning negative results.
Confirmed cases include a brown skua found in Esperance, WA, on June 14, a giant petrel on South Australia's Fleurieu Peninsula on June 14, and a giant petrel in Esperance on June 18.
Ground-based surveillance and drone surveys continue across the country.
A temporary ban on poultry products from Australia imposed by Papua New Guinea's National Agriculture and Quarantine Inspection Authority on Monday has been lifted.
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