The Australian Rural Fire Service has lost contact with a large air tanker that was operating in the Snowy Monaro area, the NSW Rural Fire Service reported.
Local media have reported that three firefighters have died in the crash.
The body assumes that the aircraft suffered a crash. The authorities are now conducting a search with the help of helicopters.
Many areas of New South Wales have continued to suffer from the bushfires, which are considered some of the most devastating in the history of Australia.
As fires are ravaging across New South Wales, Canberra airport has been shut due to the emergency, the authorities say.
In some places, the fires have become so furious that it is almost impossible to put them down from the air.