Military helicopters were called in Tuesday to help evacuate hundreds of Australians stranded by rising floodwaters, as entire towns were inundated by the worst deluges in parts of the region in decades.

Torrential rains following in the wake of tropical cyclone Tasha, which last week crossed into the northeastern state of Queensland before quickly fading, have swollen rivers and flooded scores of farms and homes in the state.

Some towns saw their worst floods in 50 years, including Theodore some 400 kilometres (250 miles) northwest of Brisbane, which has been cut off for two days and whose 350 residents were being evacuated by helicopter.

Local Banana Shire Council Mayor Maureen Clancy said the town was "just a sea of water", telling Australian news agency AAP that floodwaters had even reached its evacuation centre.

"Following a request from Queensland, the government is providing two Blackhawk helicopters to assist in the evacuation of Theodore," Prime Minister Julia Gillard said in a statement.

"Australian Defence Force personnel are on stand-by to offer further support if required."

By early afternoon, the Dawson River at Theodore was at 14.59 metres (48 feet) and rising -- way beyond the town's 1956 record of 14.07 metres -- and most of the town under water.

As many as 1,000 people have been forced from their homes by the waters, which has affected large parts of central and southern Queensland, with more than 100 homes and businesses inundated.

Officials said while the rain was abating in some places, a vast amount of water upstream was yet to flow through the towns as it made its way to the sea.

"There's an enormous amount of water still coming and I think that's the problem, the unknown we've got to face," Western Downs Mayor Ray Brown told ABC Radio after touring affected communities by air.

The Queensland government has declared several areas, including Theodore, Chinchilla and Dalby, disaster zones -- a move that gives police the power to force people from their homes if necessary.

"We are facing a really significant event here right across many parts of Queensland -- a lot of flooding, a lot of people isolated, a lot of evacuations now occurring and a lot more rain to come," Emergency Services Minister Neil Roberts said.

The floods are estimated to have cost grain farmers more than 400 million US dollars, while the crisis has closed hundreds of roads, shutting down parts of major highways.

The government said that it would provide assistance to communities affected by the flooding, helping restore essential infrastructure such as roads, bridges and schools.

"While conditions across much of Queensland have eased, the threat from floodwaters remains in many areas," Gillard said, adding that while authorities had evacuated some people, other communities remained stranded.

Police have warned residents not to attempt to drive through waterlogged roads, after they were forced to rescue several people from vehicles -- including two adults and two toddlers who were forced to cling to trees after their car was swept away.

They also arrested three teenagers after they attempted to use inflatable mattresses in a "foolish and dangerous" attempt to ride floodwaters for 30 kilometres to get to Brisbane on Monday.

"It's tomfoolery ... people on li-los (inflatable mattresses) floating down rivers, it's madness, we implore people to stop the silliness," assistant police commissioner Brett Pointing said.