Australian city braces for flood disaster (VIDEO)

Authorities ordered the evacuations of Brisbane, Australia's third-largest city, as torrential rain threatened the worst flooding in 37 years on Tuesday, while also declaring three-quarters of the state of Queensland a disaster zone.

The Brisbane River looked set to rise above the historic 1974 flood level as heavy rain, overflow from the giant Wivenhoe Dam and high tides looked set to combine to cause a major flood peak in both Brisbane and the nearby city of Ipswich over the next two days.

Panicked residents stocked up on groceries and other supplies Tuesday as the authorities urged them to remain calm.

Officials urged those in low-lying areas to move to higher ground and ordered evacuation centers set up for people who had nowhere else to go.

"We are facing one of our toughest ever tests, we will only pass this test if we are calm," Queensland Premier Anna Bligh told the Australian Broadcast Corporation. "Now is not a time for panic, it is a time for us to stick together."

On Monday, an "inland instant tsunami" of mud and water swept vehicles and people through the regional center of Toowoomba, 80 miles west of Brisbane, killing 10 people, including five children.

Up to 78 people were still missing late Tuesday, and police warned that they had “very grave fears” for their safety.

At least 20 people have been killed in the floodwaters cause by torrential rains across vast areas of Australia’s northeastern Queensland state since late December.

Officials at Australia’s Bureau of Meteorology have warned that the region’s soil has lost its capacity to absorb more water, causing floods in an area roughly the size of France and Germany — or Texas and Oklahoma — combined.

The flooding has also devastated the state's coal industry, forcing the sector's biggest producers to suspend sales and production until waters recede and rail corridors to Queensland ports reopen.

Australia accounts for over half of global exports of coking coal, used for steel making, according to Reuters. The nation is also the second-biggest exporter behind Indonesia of thermal coal, used for power generation. The wet weather has driven up long-term pricing for coking coal for the first half of 2011.

Crops have also been devastated, and Queensland residents are now facing billions of dollars in damages and lost income as a result of the flooding.

Large parts of Brisbane are already affected by flooding. A number of shops in the central business district have been evacuated and the authorities said Tuesday that about 6,500 properties were at risk of flooding.

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