SYDNEY -- Authorities have warned that supplies of Australian dairy products could be significantly affected by the ongoing bushfire disaster, which has already wiped out vast numbers of livestock.

While the full extent of the damage could take days or weeks to emerge, the Department of Primary Industries (DPI) in the badly affected New South Wales (NSW) revealed on Monday that 3,900 livestock animals had been confirmed dead so far.

Most of the losses have occurred since Christmas as fires took hold in dairy and sheep farming communities on NSW's south coast.

"Limited access to fireground and loss of power and phones in the area mean the full picture of losses and damage will take some time to emerge," State Incident Controller Karen Roberts said.

"However stock losses as a result of fires in south-east NSW since Christmas have been high, with approximately 2,800 stock reported killed in the fires or euthanized to date."

Australia exports large amounts of dairy products like milk, cheese and infant powder to countries including China.

South Coast dairy farmer Robert Miller told the Australian Broadcasting Corporation that supplies of fresh milk were likely to be significantly compromised as a result of the disaster.

"Every dairy farmer in NSW is suffering now. We've got a shortage of milk and it's only going to get worse," Miller said.

The DPI offered assistance to farmers affected by the fires, providing them with emergency fodder and water, animal care, livestock assessment, necessary stock euthanasia and burial.

"I would urge people whose stock and properties have been affected to register... so that we can allocate resources to help them deal with what are going to be very significant impacts," Roberts said.