An aerial photo taken from a helicopter shows an extensively flooded area in the New South Wales town of Moree.

Prime Minister Julia Gillard said eight military helicopters would help in search, evacuation and resupply missions in the eastern state, where days of heavy rainfall have prompted hundreds of evacuations and dozens of rescues.

"The helicopters will be available to assist in rescue operations as required until the immediate crisis has passed," Gillard said in a statement.

In the inland Queensland town of Charleville authorities are on alert amid fears a temporary levee will collapse as the Warrego River continues to rise, flooding the whole town.

The weather bureau's Paul Birch told the ABC the situation was "touch and go" as the water will be "rushing in quick over the levee".

"If it does that you find it tends to erode out part of the levee fairly quickly. So then it will just open up the river into town -- it's quite catastrophic," Birch said.

Mayor Mark O'Brien said hundreds of people had been evacuated from their homes but so far Charleville itself was "high and dry".

"We've just got an enormous body of water going down the river, but if this thing passes quickly people can just go straight back to the way they were before," he told the ABC.

In the town of Roma to the east, police were continuing their search for a woman missing since Friday after her vehicle was swept off the side of a road.

"A boy was rescued from the car and a woman got out of the vehicle but rescuers could not keep hold of her," police said in a statement. "The woman was swept away in fast flowing flood waters."

Queensland Premier Anna Bligh, who just over a year ago was dealing with epic floods that swamped the state, sweeping away entire hamlets and flooding thousands of homes, has warned the community faced dangerous new territory.

In New South Wales, the State Emergency Service said 16,550 people were stranded with the worst affected areas around Moree in the state's far north where floodwaters are expected to remain at their peak for one or two days.

"At this height the properties on the north side of the Mehi River in Moree will remain isolated with many properties surrounded by floodwater and some, possibly in excess of three hundred, inundated," the service said.

SES assistant commissioner Andrew Edwards said while the rain was easing, the amount of flooding in the region and to the north meant that "we can expect these floods to be going on for months" in some pockets.

Australia suffered epic floods late 2010 and in the January 2011 which swamped a huge area of Queensland, inundating thousands of homes and businesses, sweeping away small villages and leaving more than 30 people dead.