Floods that ravaged Australia's northeast and swamped a major city could be the country's most expensive natural disaster ever, the government said Monday.

Flooding inundated new areas in the south Monday, where water seeped into the streets of rural communities in Victoria state. Three weeks of flooding have already torn a devastating path through the northeastern state of Queensland.

The region's key Murray-Darling river basin links Queensland with New South Wales and Victoria to the south, and drains into the sea via South Australia on the south-central coast.

Queensland Premier Anna Bligh said Monday that the bodies of two more flood victims had been found, bringing the death toll from Queensland's disaster to 30, most of whom died in a flash flood that hit towns west of the state capital, Brisbane. The flooding in the state left a vast territory underwater, inundated 30,000 homes and businesses and left 12 people missing.

The price tag from the relentless floods was already at $5 billion before muddy brown waters swamped Brisbane.

"It looks like this is possibly going to be, in economic terms, the largest natural disaster in our history," federal Treasurer Wayne Swan told Australian Broadcasting Corp. Radio on Monday. "It will involve billions of dollars of commonwealth money and also state government money, and there's going to be impacts on local governments as well."

And the flooding is not finished. Victoria State Emergency Services spokeswoman Natasha Duckett warned that the town of Horsham could face a major flood during Tuesday's expected peak of the Wimmera River, and electricity supplier Powercor was sandbagging its substation there to ensure it remained dry.

"The township could be bisected with a waterway right through the middle of town and the (Western) Highway cut," Duckett said.

Up to 500 properties in the town of about 14,000 people could be affected.

Horsham official David Eltringham said the town was expecting "a one-in-a-100-year flood."

More than 3,500 people have evacuated their homes in north-central Victoria state, with 43 towns and 1,500 properties already affected by rising waters.

Flooding has also hit New South Wales, where nearly 7,000 people are reliant on airdrops of food and other supplies after being isolated by floodwaters.