Record rains that began in November left huge parts of Australia's northeast Queensland state under water, killing 30 people, damaging or destroying 30,000 homes and businesses and causing at least 3 billion Australian dollars ($3 billion) in damage to crops and lost coal exports.
The flood disaster is now moving across southeast Victoria state, where driving rains have forced swollen rivers over their banks.
The State Emergency Service has warned that a vast inland sea about 55 miles long northwest of the Victorian capital of Melbourne will continue coursing inland for the next week until it spills into the Murray River.
Emergency services were focusing their efforts 210 miles northwest of Melbourne at Swan Hill, a town of 10,000 where the Murray meets the swollen Loddon River and flood waters are expected to peak mid week, the State Emergency Service said.
Volunteers have spent the past 10 days piling tens of thousands of sandbags around the community, Mayor Greg Cruickshank said Monday.
"We're nearly to the point to where we are as prepared as we can be," he said. "If there happens to be inundation, it certainly won't be for lack of trying."
Several hundred residents were evacuated Sunday from tiny communities east of Swan Hill, including Pental Island, where about 50 properties were expected to become isolated or inundated.
On Monday, some residents of the small community of Murrabit West, about 30 miles east of Swan Hill, were urged to evacuate as water from the Murray began spilling over the levees protecting the township. An emergency service spokeswoman said officials did not yet know how many homes were at risk of being flooded.
Deputy Prime Minister Wayne Swan said in a statement Sunday that the floods will rank as one of the most costly natural disasters in Australian history and its impact on the economy will be felt for years.
The government will announce its first cost estimates on Friday, he said.
Swan and Prime Minister Julia Gillard were in the Queensland capital of Brisbane on Monday for a meeting of Gillard's business taskforce, which was set up following the Queensland floods to encourage companies to donate to relief efforts.
"We still don't know what the total damage bill is," Gillard said. "We've got to be very clear here - the federal government is going to step up and do everything we need to do to rebuild Queensland."
The State Emergency Service said Monday that 76 towns in Victoria have been affected by flooding, with 1,770 properties suffering some water damage. Another five to 10 towns are still in the floodwaters' northern path across flat wheat-growing country.