An unidentified strain of bird flu has been detected at a hen farm near Maitland in the Hunter Valley, prompting authorities to quarantine about 50,000 chickens.
The suspected virus is not thought to be the deadly H5N1 strain of bird flu that has killed 359 people worldwide in sporadic outbreaks since 2003.
Nonetheless, the 50,000 hens may have to be destroyed, the NSW Department of Primary Industries said.
A "first response team" of specialists from the department is on site to enforce the quarantine, while the CSIRO runs lab tests on samples of the virus, with results expected this afternoon.
"The suspected virus is definitely not the highly pathogenic H5N1 strain that has gained worldwide attention — nor is it closely related to that strain," the NSW chief veterinary officer, Ian Roth, said in a statement.
"Australia has previously had a small number of outbreaks of avian influenza viruses, which were all quickly and successfully eradicated," Dr Roth said.
"The property has been placed under quarantine and initial tracing and surveillance is being undertaken to confirm that the virus hasn't spread. We currently have no evidence to suggest it has."
The department said Australia has had five outbreaks of avian influenza in chickens between 1976 and 1997 – three in Victoria and one each in NSW and Queensland.
"All the outbreaks were contained and successfully eradicated with no impact on human health," it said. "They were not caused by the H5N1 strain. They were all from an H7 strain."