Emergency workers and volunteers carry sandbags to protect a house from rising floodwaters near Echuca in Australia's Victoria state. ((Associated Press))

Australia's deadly flood crisis forced more people to flee their homes Monday as a vast swath of muddy water spread farther across the country's southeast, threatening to swamp several rural communities.

Record rains that began in November have 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 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 90 kilometres 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 about 340 kilometres northwest of Melbourne at Swan Hill, a town of 10,000 where the Murray meets the swollen Loddon River and floodwaters are expected to peak at 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.

Isolation expected

"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 removed 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 50 kilometres east of Swan Hill, were urged to leave 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 Sunday that the floods will rank as one of the most costly natural disasters in Australian history and their impact on the economy will be felt for years.

The government will announce its first cost estimates Friday, he said in a release.

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 after 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 76 towns in Victoria have been affected by flooding, with 1,770 properties suffering some water damage. Another five to 10 towns are in the floodwaters' northern path across flat wheat-growing country.