"Worse to come" in Brisbane flood disaster (VIDEO)

Thousands of Brisbane residents are rushing to higher ground as floodwaters threaten to swamp as many as 20,000 properties in Australia's third-largest city.

Others in the city on Wednesday hoarded flashlights, batteries and any other emergency supplies left at grocery store shelves emptied by panic buying, after officials said the worst of the flooding was yet to come. Though the Brisbane River has already broken its banks, the peak isn't expected until sunrise Thursday.

About two million people live in Brisbane, the latest city to be affected by devastating flooding that has inundated a large swath of Australia's northeastern Queensland state. A map of the flood-region shows an area the size of France and Germany combined.

The state premier, Anna Bligh, told reporters that the death toll from the flooding had risen to 12, but that a further 67 people had been reported missing. "We are preparing for the worst natural disaster in our history," Bligh said.

Deputy Police Commissioner Ian Stewart told The Sydney Morning Herald that recovery teams were searching buildings "completely destroyed" by floodwaters, and combing trees, creeks and cars for bodies.

"Our hope is that we actually might find some survivors but the chances of that are quite remote," he said.

Focus has shifted in the past 24 hours from the regional city of Toowoomba, 80 miles west of Brisbane, where flash flooding described as an "inland instant tsunami" swept 12 people to their deaths on Monday and Tuesday.

Brisbane residents were told to evacuate homes early, but many were caught off guard by the speed of the rising water, which is not expected to peak until early Thursday and which is then expected to remain at high levels for days.

On Wednesday, residents contacted by GlobalPost described seeing not only boats torn from their moorings floated down the rising Brisbane River, but whole pontoons, along with massive amounts of debris.

The flooding is shaping up to become one of the nation's most expensive disasters, costing about $5 billion. The floods have affected about 200,000 people, shut down Queensland state's crucial coal industry and ruined crops across vast swaths of farmland.

Up to 1 percent could be cut from Australia's economic growth in 2011 as a result of the flooding, according to a board member of the Reserve Bank of Australia.