The Queen has extended her "sincere sympathies" to hundreds of thousands of Australians hit by floods in Queensland.
Military aircraft have dropped supplies to the 200,000 inhabitants of towns cut off by the rising tide of water, which covers an area larger than France and Germany combined.
An estimated 22 towns have been left isolated or inundated by the rising waters, with fears that damage could cost billions of Australian dollars to repair.
The Queen issued a statement saying: "I have been following with great concern over the last few days the news of the devastating floods in Queensland.
"Please extend my sincere sympathies to all the people whose communities and livelihoods have been so badly damaged in this disaster."
The Queen's message was sent to Queensland Governor Penelope Wensley as Australian prime minister Julia Gillard toured an evacuation centre in the flood-stricken town of Bundaberg.
Families whose homes were flooded or damaged are eligible for relief payments of 1,000 Australian dollars (650) per adult and 400 dollars (260) per child, she announced.
"My concern is for the people in these very difficult times," Ms Gillard said.
The premier had already pledged one million Australian dollars (650,000) in federal aid to match a relief fund the state government had already established.
Half of Queensland's 715,305 square miles is affected by the flooding, officials said.
The disaster began to unfold last week when swollen rivers overflowed after days of relentless rain.
While the rain has stopped, the rivers are surging to new heights and spilling into low-lying towns as the water makes its way toward the sea.
There is a shortage of drinking water and fears over mosquito-borne disease because thousands of homes and businesses have been swamped with muddy water.
Queensland premier Anna Bligh said: "This is without a doubt a tragedy on an unprecedented scale."
Ms Bligh warned that drenched communities could be stuck under water for more than a week, and clean-up efforts were expected to cost billions of dollars.
Supplies of food and bedding were delivered by road and by military aircraft yesterday to the towns of Rockhampton, Emerald, Springsure and Blackwater in central-east Queensland.
Forced evacuations are being planned in Rockhampton as rising floodwaters threaten the town of 77,000 and the situation in Emerald – a town of some 11,000 people – was particularly bad, Ms Bligh said.
Helicopters including army Black Hawks have been used to ferry residents to safer locations.
More than half of Queensland is now a disaster zone.
Two smaller towns, Theodore and Condamine, have been completely evacuated.
In Condamine some residents had been refusing to leave their houses.
Ms Gillard said: "As devastating as these floods are, we are seeing a magnificent response by all levels of government and by emergency personnel."
Recovery work following the floods is expected to cost billions of dollars.
Officials are warning of severe damage to homes, crops and livestock.
Sewerage systems have also been affected, raising public health concerns.
Rockhampton resident Petros Khalesirad said: "These floods are going to affect the state, the whole nation.
"It's going to have a huge impact on mining commodities – several coal mines are under water and some won't be operational for months."