The fire gutted most of the buildings on Carngham Station, including the two-story brick manor house built in the 19th century, the Herald Sun of Melbourne reported. The homestead, now a horse-breeding operation, is near Ballarat in Victoria.
Ron Bolton, the gardener, who lives in the only surviving house, said burning embers began falling on the property in the middle of the night. He told the Herald Sun it was "just too hot" for firefighters to save most of the buildings.
Bolton said the house burned quickly after it caught fire. By morning, all that was left was still-smoking debris, some brick walls and a bathtub visible.
"There's not a scrap of timber left in the place, not even the staircase," Bolton said.
Ian Morley of the Country Fire Authority said the fire that destroyed Carngham Station and four other homes is believed to have been caused accidentally by a farmer's utility vehicle.
Much of Australia has been hit by recent bush fires, including the eastern states of Victoria, New South Wales and Queensland, Tasmania and West Australia.