National Farmers Federation President Peter Corish said there had been no significant rain "in virtually all areas," raising the prospect of hundreds of millions of dollars in losses.
"There has been very little winter crop planted," he said. "If we don't see some significant falls in the next couple of weeks the chances of a normal winter crop are going to be very much reduced."
Corish said pasture conditions and water stocks in New South Wales and southern Queensland also had deteriorated "very rapidly."
Government economist Craig James said worsening farming conditions threatened Australia's economic outlook, both through the direct impact of lower farm production and the indirect impact of lower spending.
"Australian retailers have faced challenging conditions over the past three years, with autumn and winter temperatures as much as 3 degrees above normal," James said.
"If autumn and winter turn out to be warmer and drier than usual, there is reduced consumer enthusiasm for seasonal food and clothing items as well as goods such as heaters and blankets."