Floodwaters have forced most of Queensland state's coal mines to shut and some may not restart production for months, ministers said at an emergency Cabinet meeting in Brisbane.
Queensland Premier Anna Bligh announced that Major General Mick Slater would lead the recovery effort from the floods that have affected 200,000 people.
"This is a disaster of an unprecedented scale and it will require an unparalleled rebuilding effort," said Ms Bligh . She added that until the waters dried up, it would not be clear what the cost of the flooding would be.
"If you count everything from the cost to homes, the home rebuilding effort, public infrastructure rebuilding effort and economic loss, I think we're well above $5bn (3.2bn) territory," she said.
Queensland is a centre of Australia's coal mining industry and 40 mines have been shut because of the flooding.
Resources minister Stephen Robertson said: "It's going to take some months for some mines to be back to full operation. We earn round about $100m (64m) a day exporting coal to the rest of the world and exports have been significantly restricted by the impact on infrastructure."
Ms Bligh also said the deluge has ruined crops and caused "catastrophic" damage to Queensland's transport systems.
More than a week of pounding rains that started just before Christmas left much of north-eastern Australia under a sea of water that is making its way through river systems toward the ocean.
Around 1,200 homes in Queensland have been inundated, with another 10,700 suffering some damage. Four thousand residents fled their homes in the flood zone, which spans an area greater than France and Germany combined.
The coastal city of Rockhampton has been particularly hard hit. Exhausted residents were warned they would face a long wait before the muddy mess dried up but there was hope the waters had swelled to their highest level.
Water from the overflowing Fitzroy River has already swamped 200 homes and 100 businesses. "It looks like it may have stabilised," Mayor Brad Carter said. In the city of 75,000, about 500 residents were evacuated this week.
Residents face a long wait before things return to normal, officials warned.
Queensland police Acting Assistant Commissioner Alistair Dawson said: "These water levels will be consistently high for a long period of time and these levels could stay for 24 hours before they start to drop."
In other parts of the state, some flooded communities were beginning to dry out.
In the town of Theodore, which evacuated all 300 residents last week, specialists arrived in helicopters yesterday to check the safety of power, water and sewage plants, county Mayor John Hooper said.
Officials were still trying to decide when it would be safe to allow residents to return, with particular fears raised over an influx of venomous snakes, which have been flushed from their habitats and are searching for dry ground amid the waters.
Saltwater crocodiles were another worry for people entering floodwaters, as the predators have been spotted from time to time in the Fitzroy, he said.
Rockhampton resident Shane Muirhead said: "There's a lot of snakes – and I mean a lot.
"Like, every hundred yards you will see a snake, and they're just everywhere."