Fears eased Tuesday that a swollen river would breach its banks in the Australian state of Queensland as residents in other areas began a huge clean-up after floods wrecked havoc.

Thousands of Australians have been forced to abandon their homes as a record deluge sweeps through areas still reeling from devastating flooding last year that left 35 people dead.

So far, only one fatality has been reported this year although hundreds of homes and businesses have been damaged.

In the cotton-growing centre of St George, in Queensland's south, more than 2,500 residents have fled in the largest evacuation in the state's history amid concern that a levee on the Balonne River would be breached, submerging the town.

The water level had reached around 13.86 metres (45 feet 6 inches) by early morning and was creeping towards a predicted peak of around 14 metres, close to the levee height of 14.5 metres.

"It's slowed up a little bit but it's still rising and should get up to 14 metres sometime today," a Bureau of Meteorology spokesman said.

"It will take quite a few days before it really starts to drop away."

Reports said between 50 and 60 homes had been inundated in the town.

Flooding has been hitting parts of Queensland over the past week, damaging more than 500 properties in Mitchell and Roma, with residents Tuesday slowing starting to return.

Neighbouring New South Wales state has also been hit, with mass evacuations last week in Moree when flood waters inundated the town, cutting it in half.

Moree Mayor Katrina Humphries said most people had now returned to face a "vile, soul-destroying" mopping up operation with some residents losing everything.

"The long, hard recovery process has started," NSW emergency services commissioner Murray Kear told reporters.

Many rural properties across NSW remain isolated with the worst-affected area south of Moree in Wee Waa where 2,300 people are stranded, Kear said.

"Isolation is expected to continue for a further four or five days," he said.

Meanwhile, flood warnings were issued for the Namoi River at Wee Waa, as well as downstream for Boggabri and Narrabri.