Bird flu has been confirmed in a flock of 50,000 hens in the Hunter Valley and the government is enforcing a quarantine around the infected farm
Tests confirmed the birds are suffering from a strain of avian influenza, but not the deadly H5N1 version that can jump to humans.
The entire flock of 50,000 birds will be destroyed to stop the infection spreading to other birds.
The NSW Food Authority said there were no food safety issues and poultry and eggs remain safe to eat.
The state's chief veterinary officer, Ian Roth, said the farm would remain under surveillance but there was no evidence that the infection had spread.
It is the sixth outbreak of bird flu in Australia, and the second in NSW, since 1976.
The H5N1 strain of bird flu is known to have killed 359 people around the world since 2003, but the Maitland outbreak is not considered a danger to humans.