Emergency services in northern Australia are battling the worst floods in three decades as residents report shortages of supplies and crocodiles swimming through towns inundated by water.

Almost 3,000 homes have been flooded and 30 people evacuated in the northwest of Queensland state, the Department of Emergency Services said. Supplies are being airlifted to towns cut off by rising waters in the region west of Cairns, it said.

"It's like looking out into an ocean," Donna Smith, acting manager of the Albion Hotel in Normanton, a town inland from the Gulf of Carpentaria, said by telephone today. "There is a 5-meter crocodile swimming by, but the biggest problem is that we're running out of beer."

Torrential rains began three days ago as the aftermath of Tropical Cyclone Ellie crossed over northwest Queensland, triggering the worst flooding in 30 years, the Bureau of Meteorology said. Waters are expected to peak today, it said.

"It will take weeks to subside," according to Jeff Perkins, hydraulic supervisor at the flood warning center in Brisbane. "It is a very prolonged major flood."

Queensland Premier Anna Bligh said yesterday military personnel, helicopters and aircraft may be needed in the next two to three days to help with the relief effort.

Food will arrive in the worst-affected towns today, the department said in a statement. More people will probably need to be evacuated, it said.

"People are just floating along and they're pulling together and helping each other out until we get some more supplies through," Smith said from the Albion, where water is lapping at the hotel's front steps.

"It will be at least another week before we can get any alcohol through, so we're rationing at the moment and we're not selling any to take away over the counter," she added.