The H5N1 bird flu was detected in preliminary testing in a migratory bird at Hawks Nest, on the state's Mid-North Coast, authorities revealed on Friday.
More substantial testing is expected to confirm the case over the weekend, but authorities say the detection of the virus does not come as a surprise.
Five cases of the strain have been confirmed so far in seabirds in Western Australia and South Australia, along with another suspected case detected on Friday in a migratory bird in the northern Perth suburb of Mullaloo.
Surveillance and testing have been ramped up across NSW with the government working closely with industry to prevent a potentially catastrophic spread.
While the virus can be deadly for animals, the risk to humans is generally considered low both in terms of transmission and health impact, the state's chief veterinary officer Jo Coombe told reporters.
Dr Coombe described the symptoms of the virus in humans as being similar to a common cold, adding there had been no recorded cases of human-to-human transmission.
But a high number of deaths in wildlife and agricultural populations had been recorded in areas where the disease has run rampant overseas, she said.
"It's had devastating impact overseas," she said.
"There have been hundreds of species of birds affected, and also over 50 species of mammals.
"It can affect humans, but this particular strain is deemed to be very low risk to humans."
Samples from a giant petrel near Hawks Nest, a town about 228km north of Sydney, tested positive for H5N1 influenza in preliminary testing after a member of the public reported the animal as looking unwell.
Dr Coombe said the species generally migrate north from the southern ocean and don't make landfall unless they are sick or have something wrong with them.
There were no reports of the poultry industry being impacted but producers had been informed of the new case and advised to increase biosecurity measures, NSW Agriculture Minister Tara Moriarty said.
"I do want to be clear with the community, this is one bird, a wild migratory bird that has been found," she said.
No mandatory enforcement measures have been imposed on industry.
"The government is working very closely with the poultry industry, and we have been for some time - they are ready for whatever scenario might emerge," Ms Moriarty said.
"There's no need for panic buying eggs - keep buying eggs, keep buying chicken."
Surveillance by wildlife agencies is also being ramped up to help detect any further cases.
"We are using the best available data now to target actions for our most at-risk wildlife species and important natural places," Dr Coombe said.
Members of the public are being asked to report any suspected cases of the flu in wild birds and reminded not to touch the animals themselves.
Until June, Australia had been the only continent free of the highly contagious virus, which has wiped out millions of birds worldwide and also killed mammals.
The strain was first detected on the Australian mainland on June 14 in a brown skua found in Esperance, on WA's south coast.
All positive cases have occurred in wild birds, with no signs the virus has spread to local poultry populations.
The sudden increase in detections in Australia could be the result of changes in weather patterns which might have pushed the birds off course and closer to the Australian coast.
People are being 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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