The deadly H5N1 strain has now been confirmed in a migratory bird in NSW, making it Australia's sixth confirmed case after five others were discovered in Western Australia and South Australia.
"Testing at CSIRO's Australian Centre for Disease Preparedness has confirmed H5 high pathogenicity avian influenza (bird flu) in a sample taken from a giant petrel found near Hawks Nest in New South Wales," a statement from Australia's chief veterinary officer Sam Hamilton said on Saturday night.
"This is the sixth detection of H5 bird flu in migratory seabirds."
Another suspected case was detected on Friday in a migratory bird in the northern Perth suburb of Mullaloo, and further testing is under way.
"There remains no evidence of any mass mortality events and there are no detections in poultry or in our agricultural production system," Dr Hamilton's statement said.
"The risk to human health remains low."
Australia's technical body for animal health emergencies has said commercial poultry producers might want to keep free-range birds indoors for the next two weeks while the biosecurity threat was fully assessed.
Dr Hamilton, also acting chair of the Consultative Committee on Emergency Animal Diseases, said farmers should only consider housing hens if it was practical and did not impinge on animal welfare.
He said it would be up to states and territories to endorse the body's non-mandatory recommendation.
"There have only been detections in migratory seabirds that occasionally visit Australia," he said after the emergency animal diseases committee met on Friday.
NSW Agriculture Minister Tara Moriarty said her government's response to the latest confirmed case includes ramped-up surveillance of high-risk areas and extra staff deployed to support industry and the community.
"At this stage the result is limited to a single migratory seabird and has not impacted our poultry sector or domestic wildlife," she said in a statement.
"There is no impact on the supply of chicken meat or eggs and I would encourage everyone to purchase these products as they normally would."
Burnet Institute scientific director for research translation Heidi Drummer said the case in Hawks Nest, on the NSW Mid-North Coast, was significant, but there was no reason to panic.
Professor Drummer said careful surveillance and testing were crucial as authorities tried to determine whether the detections in migratory seabirds were isolated events or part of a broader pattern of virus movement in wild bird populations.
"It is important to be clear that detection in wild birds does not mean the virus is widespread in Australia, or that it has entered commercial poultry," she said.
The strain was first detected on the Australian mainland on June 14 in a brown skua found in Esperance, on WA's south coast.
The spread among migratory birds was "largely inevitable" but Australia was still doing "a very good job" of containing bird flu, Mater Health Services director of infectious diseases Paul Griffin said.
Professor Griffin said it was now "only a matter of time" before further cases were detected in other states, and the impact on commercial bird populations could be devastating if large-scale culls were required.
"But we do have good protocols in place … some of the largest producers have implemented more stringent measures to reduce that risk," he said.
Emma Grant, from La Trobe University's Institute for Molecular Science, said the virus could spread very quickly.
"It can also be quite severe in different animals, so what it means for the wildlife in Australia is yet to be seen," Dr Grant said.
The public has been urged to avoid contact with sick or dead wildlife, report any finds to an emergency hotline, record locations and take photos.
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