Two horses have been confirmed positive for equine influenza on a property at Barmedman in the previously disease-free green zone.
NSW deputy Chief Veterinary Officer Steve Dunn said staff were investigating the exact cause of the isolated outbreak, and any possibility of disease spread.
"This property is located between West Wyalong and Temora, and about 40 km from the boundary of the amber zone," Mr Dunn said.
"The horse owners in this case took early action by reporting their sick animals immediately, which hopefully will give us a better chance of preventing further spread.
"A red zone is being declared around the property and the amber zone will be extended further west and south.
"This will unfortunately restrict the movement of some horses which were recently given greater freedom to move when the zones were declared."
Mr Dunn said it was important to keep as much of NSW EI free as possible.
"This setback reinforces the need for strict biosecurity when people come in contact with horses," he said.
"The horse flu virus is very contagious because it can live on your body and your clothes for up to 48 hours and can be transmitted from humans to horses.
"The most effective way is to wash your hands and arms thoroughly, blow your nose, wash your clothes, and change your clothes.
"If it is essential you have contact with another horse, do so with clean outer garments and having followed these basic hygiene procedures".
- NSW Dept of Primary Industries
NSW deputy Chief Veterinary Officer Steve Dunn said staff were investigating the exact cause of the isolated outbreak, and any possibility of disease spread.
"This property is located between West Wyalong and Temora, and about 40 km from the boundary of the amber zone," Mr Dunn said.
"The horse owners in this case took early action by reporting their sick animals immediately, which hopefully will give us a better chance of preventing further spread.
"A red zone is being declared around the property and the amber zone will be extended further west and south.
"This will unfortunately restrict the movement of some horses which were recently given greater freedom to move when the zones were declared."
Mr Dunn said it was important to keep as much of NSW EI free as possible.
"This setback reinforces the need for strict biosecurity when people come in contact with horses," he said.
"The horse flu virus is very contagious because it can live on your body and your clothes for up to 48 hours and can be transmitted from humans to horses.
"The most effective way is to wash your hands and arms thoroughly, blow your nose, wash your clothes, and change your clothes.
"If it is essential you have contact with another horse, do so with clean outer garments and having followed these basic hygiene procedures".
- NSW Dept of Primary Industries