More storms are forecast for Queensland. Twenty two towns are already cut off or flooded and more than 200,000 people affected.
Queensland police say the scale is enormous. The floods now cover an area bigger than New South Wales.
Waters are receding in some areas, but the Fitzroy River is still rising in Rockhampton - a city of 77,000.
Floodwaters there could reach nine metres on Monday and peak at 9.4 metres on Wednesday.
The ABC reports up to 400 homes could go under by the middle of the week.
The Bureau of Meteorology said a severe thunderstorm late on Sunday night would bring "winds, very heavy rainfall, flash flooding and large hailstones" to areas including Charleville, Emerald and Blackwater.
The BBC reports residents in Rockhampton have been leaving their homes for days already.
Mayor Brad Carter has warned that about 40% of the city could be affected.
He told Summer Report that the situation facing the community is very serious.
He said about 400 people have been relocated.
The airport is closed to commercial flights and roads into the city from the south and the west are cut.
Residents in Bundaberg are now returning to their homes. More than 400 houses and businesses were inundated when the Burnett River peaked at 7.9 metres on Thursday.
The ABC reports the river has now fallen, revealing widespread damage.
Bundaberg Regional Council says it will be weeks before the full cost of flood damage to the region is known.
State Treasurer Andrew Fraser has described the flooding as a disaster of "biblical proportions" and said the economic impact would be severe.
Mr Fraser said the ultimate cost would exceed A$1 billion.
"The cost to the state will be huge - both in direct costs such as rebuilding roads, and other damaged infrastructure and providing relief payments to families - but also in lost income, while the mining, agriculture and tourism sectors recover," he said.