Plea for calm over mass bird flu cull 

Almost a quarter of a million birds will be killed on a New South Wales farm in an attempt to stop the spread of the state's bird flu outbreak.

The orders comes after avian influenza was picked up on a mixed barnyard and free-range poultry farm in the Hawkesbury district, northwest of Sydney.

The highly contagious and deadly H7N8 strain of the virus has already killed 8000 birds at the facility over the past 48 hours, the state government said in a statement on Thursday.

More than one million chickens and ducks are also set to die in Victoria after the highly pathogenic strain H7N3 was found on multiple properties in the state during the week.

NSW officials engaged the state's emergency biosecurity incident plan, sending the farm into quarantine and triggering movement controls in the area.

A control order to depopulate the farm of its birds "in a humanely manner" and to securely dispose of the remains has also been issued.

It will take up to a week for 240,000 birds to be destroyed at the farm.

Another control order to legally lock down movement of machinery, materials, animals and transport within a radius of 2km around the affected egg farm will be issued later on Thursday.

The lockdown order will cover three other commercial poultry farms with up to 355,000 birds, which will be monitored for any signs of the virus.

Impacted producers will be compensated through a funding agreement with the Commonwealth, egg industry and other states.

Agriculture Minister Tara Moriarty said people should not be concerned about eggs and poultry products from supermarkets, saying the detection did not mean there was a risk to public health.

Premier Chris Minns called for calm, saying he did not anticipate any challenges to supply.

"There's no reason to panic in relation to this," he told reporters.

"The information that we've received from the experts who are tasked with setting up a quarantine and ensuring the safety of agricultural products is that it's contained to this one site."

Health Minister Ryan Park said the virus did not transmit easily between people or from animal to human.

"This presents like many other flus and provides those sort of flu-like symptoms that people get," he said.

"We've got to just stay calm about this ... NSW Health and Primary Industries are working together on the situation."

Both strains detected in Australia are different to the H5N1 strain that has infected billions of wild and farmed animals globally, raising fears of human transmission.