Flood waters rose Monday in parts of Queensland as the Australian state raced to complete the largest evacuation in its history with police boosting their presence to prevent looting.

Thousands of Australians have been forced to abandon their homes as a record deluge sweeps through areas still reeling from last year's devastating flooding.

The area in most danger Monday was the town of St George, in Queensland's south, with most of its residents fleeing Sunday evening, although some 400 have stayed to help limit the damage despite a mandatory evacuation order.

Local mayor Donna Stewart said the swollen Balonne River in St George, flooding for the third time in less than two years, had reached 13.48 metres (44 feet) and was expected to keep rising until at least Tuesday night.

Forecasters have estimated it could top 15 metres, breaching the town's 14.5-metre levee, with fears mounting for other small towns south of St George, including Cunnamulla and Dirranbandi.

State Premier Anna Bligh said it was not looking good.

"The town of St George has no prospect of holding back that water with the levee that they built," she told ABC radio, but said there had been no "panic or disorderly behaviour".

It had been the largest ever evacuation of a town in Queensland, she added.

"The heartbreaking job of calculating the loss is still in its early stages," she said.

Reports said about 30 houses and business had been inundated so far.

The Australian Broadcasting Corporation said the Moonie Highway on the outskirts of town was now flooded and the only way out was by air.

"There will be more planes and we expect to take about another 400 (residents) out today, so in a town of just under 3,000 people we don't expect to see very many people stay," added Bligh.

While most residents have fled, Queensland Police Commissioner Bob Atkinson said officers would stay to prevent looting.

"We are going to do everything we can to make sure people's homes are safe," he told reporters.

St George has seen major flooding twice in the past two years, once in March 2010 and again last year during Queensland's flooding disaster, which claimed 35 lives and swamped vast tracts of farmland and tens of thousands of homes.

Flooding has been hitting parts of Queensland over the past week but has claimed just one life, a woman whose car was swept from a roadway in Roma, further north of St George.

An 18-month-old baby girl drowned in a dam on a property south of St George, although authorities said it was not directly linked to the floods.