Hundreds of people fled worsening floods in Australia's rural northeast Thursday as officials warned the disaster may last for weeks, prompting fears over food shortages and disease outbreaks.

The latest evacuees, including 100 residents air-lifted from one town, join over 1,000 moved earlier, while thousands more braced for large-scale inundations in the regional centres of Emerald, Bundaberg and Rockhampton.

As displaced residents sheltered in makeshift relief centres or with friends and relatives in the farming and coal-mining region, Queensland premier Anna Bligh warned the state was facing its "toughest hour".

"This is a disaster on an unprecedented scale," Bligh told reporters. "What we've never seen is so many towns, so many communities, so many regions all affected at once. It is a miserable and heart-breaking event," she added.

Tropical cyclone Tasha caused widespread flooding over Christmas in the economically important zone near Brisbane, with rivers now swelling to record levels as rainwater flows downstream.

Some 80 percent of Emerald, population 11,000, is expected to be flooded after a nearby river reached record levels, while Bundaberg has been split in two by the inundation and 4,000 Rockhampton properties could also be hit.

On Thursday, all 100 residents of rural Condamine were air-lifted to safety, while officials said they may need to drop food by plane to areas cut off by the crisis.

"Some of those bigger centres, which will require significant volumes of food and groceries... may well have become a significant problem," State Recovery Co-ordinator Bruce Grady told reporters.

"We may have to look at creative ways to do that. We have to look at moving produce by sea, plane," he said.

Meanwhile officials said water contaminated by sewage and rotting animal carcasses could pose a serious disease risk, along with mosquitoes breeding in the large pools.

"One of the main reasons everyone had to evacuate was the water, sewage and the health risks," Banana Shire acting mayor Maureen Clancy told the Courier-Mail newspaper.

Bligh said the damage bill would run into several billions of dollars (several billion US) and warned floodwaters may not recede for another 10 days, with relief and clean-up operations potentially lasting weeks.

"We've got a long way to go ahead of us and when these waters recede, that is when we're really going to know the size of the problem," she told reporters.

"That is when many people will get back into their homes and it will really hit them just how many of their precious family possessions have been washed away forever," she added.

Global miners Rio Tinto, BHP Billiton and Anglo American declared "force majeure" at various coal projects, meaning production may be affected, while swathes of cotton and sugar-cane farmland have disappeared under the waters.

Elsewhere in Queensland, police feared the monsoonal downpour had claimed its first life after the body of a 50-year-old man, believed drowned, was fished out of a swollen river near Cairns.

Large parts of the state have been declared natural disaster areas, giving them access to emergency funds, while reports said the damage could send prices of melons, tomatoes, mangoes and bananas soaring.

Queensland Shark Control Program manager Tony Ham also told the Courier-Mail that floods may have flushed bull sharks out of major rivers and into popular swimming and surfing spots. Similar warnings have been given about crocodiles.

The floods have caused serious damage to infrastructure, swamping rail lines and washing away roads, while Rockhampton's airport is also under threat of closure.

Meanwhile weather forecasters warned that another cyclone was forming off Western Australia, on the other side of the huge country, while extreme heat posed a wildfire risk in South Australia and Victoria over New Year.