A giant inland sea fed by the heavy rains that have swamped eastern Australia is spreading through Victoria state, threatening rural communities.
Emergency services are focusing on Swan Hill, a town 210 miles north-west of the Victorian capital of Melbourne, where the Lodden and Murray rivers meet, and floods are expected to peak there midweek when the sea arrives.
Volunteers have spent the past week piling tens of thousands of sandbags around the town, home to 10,000 people, Mayor Greg Cruickshank said.
"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."
Australia's deadly flood crisis began with record rains in November that left huge parts of the north east state of Queensland a disaster area, killing 30 people, damaging or destroying 30,000 homes and businesses and causing at least three billion Australian dollars (£1.86 billion) damage to crops and lost coal exports. The state capital and the country's third-largest city, Brisbane, was swamped for days.
The flood disaster is now moving across south-east Victoria state, where driving rains have forced swollen rivers over their banks.
In front of the inland sea, several hundred residents were evacuated on Sunday from tiny communities east of Swan Hill, including Pental Island, where about 50 properties were expected to become isolated or inundated. At 55 miles long and 25 miles wide, the inland sea is 350 square miles larger than the French capital.
Some residents of the small community of Murrabit West, about 30 miles east of Swan Hill, have been 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 on 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.
Mr Swan and Prime Minister Julia Gillard are in Brisbane for a meeting of Ms Gillard's business task force, which was set up following the Queensland floods to encourage companies to donate to relief efforts.