People in an Australian city cut off by some of the country's worst flooding in decades are being warned to stay out of the water amid fears of snakes and even crocodiles at large.

Large parts of the coastal city of Rockhampton were under water today, with levels still rising and the 75,000-strong population bracing for the floods' expected peak in the next 24 hours as a huge inland sea spawned by heavy rain across Queensland state drains toward the ocean.

Up to 500 people have been evacuated from their homes along the Fitzroy River, which runs through the city and has spilled over its banks and inundated houses and businesses in waters ranging from a few inches to waist-deep, with levels expected to rise another few feet.

Queensland state premier Anna Bligh said all air, rail and road links to the city had been cut - though local officials said later one highway heading north was still open.

Rockhampton is the latest of 22 cities and towns in Queensland to be swamped by floods that began building just before Christmas - the worst effects of an unusually wet summer in the tropical region.

Swollen rivers and flooding have killed 10 people in Queensland since late November, police say.

Officials have said the flooded area covers the size of France and Germany combined and 200,000 people have been affected.

Authorities have warned residents to stay out of floodwaters for their own safety, saying the biggest risk is from fast-moving currents powerful enough to sweep cars from roadways - at least two people have drowned after being swept away in their cars.

Rockhampton mayor Brad Carter has also said residents have reported higher than usual numbers of snakes being seen, as the animals move around looking for dry ground. He has also noted that saltwater crocodiles have been spotted from time to time in the Fitzroy River.

"We do not think they are a risk to public safety if people keep out of the waters, but if people do enter the waters their safety cannot be guaranteed," Mr Carter was quoted as saying in The Australian newspaper.

Animal welfare worker Wendy Hilcher said fears about snakes and crocodiles were hampering her group's efforts to rescue pets left behind by people who had left their homes in flooded areas of the city.

"It's not just the safety aspect of getting to these places, it's what's in the water itself," Ms Hilcher, from the Royal Society for the Prevention of Cruelty to Animals, said.

"If it gets too dangerous, we have to get out of there."

A military cargo plane landed in a city north of Rockhampton yesterday carrying food, water, medical supplies and other items such as diapers to keep the city stocked with necessities. The goods were being trucked south to the city, or carried on barges.

Further flights would continue as needed, acting defence minister Warren Snowdon said.

Many stores and businesses in dry parts of the city remained open. Power supplies were being severed to inundated areas for safety reasons, officials said.

Prime minister Julia Gillard has said the cost will probably reach many hundreds of millions of dollars and has announced relief funding worth millions.

The rains that started the flooding have eased and water levels have been dropping in some towns in the state.

Across the state, some 1,000 are living in evacuation centres, and it may be a month before the floodwaters dry up completely.