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Whole families are unaccounted for after flash floods in southern Queensland, with eight confirmed dead and Premier Anna Bligh warning the toll could rise dramatically.
Ms Bligh said authorities were considering declaring a mega-disaster zone over a "significant region" of Queensland, a move that would be unprecedented in the state's
history.
"We are just looking for an appropriate northern line and everything south of that would be declared," she said.
The premier said four of the confirmed deaths were children, and there were fears for many other people, with 72 unaccounted for.
"We have eight confirmed deaths at this point but we expect that figure to rise and potentially quite dramatically," Ms Bligh told reporters on Tuesday.
Ms Bligh said "whole families" were unaccounted for after flash flooding hit the city of Toowoomba west of Brisbane, and the Lockyer Valley at the foot of the Toowoomba range.
"We're hoping and praying that many of those 72 people have gone to safety overnight and will be found safe and well," she said.
"But given the circumstances we hold very grave concerns for many of those people.
"... many of the people who are stranded or unaccounted for are families and young children and some of those who have lost their lives overnight are young children, including a mother and two children in a vehicle."
Ms Bligh said bad weather was hampering search efforts where people were still stranded in "dire and critical circumstances".
Specialist teams have been deployed to the region and rescue teams are on standby, as well as additional fire and rescue officers.
But weather is stopping them from being deployed, she said.
"We have a grim and desperate situation," the premier said.
"... this took everybody so unawares that there was no opportunity in most cases for people to get to safety."
Until emergency workers could reach affected areas, it would remain unclear if those forced to take shelter on roof tops in the valley had reached safety.
Evacuations continued across the Lockyer Valley on Tuesday, amid more warnings of flash flooding.
Deputy Police Commissioner Ian Stewart said there were grave concerns for the communities of Murphys Creek and Grantham.
"It is expected we will find further persons deceased in those areas. The number we just don't know at this stage," he told reporters.
Ms Bligh said the flooding west of Brisbane would have major implications for the Wivenhoe Dam, which releases water into the Brisbane River.
She said those releases were not optional and must continue to ensure the dam functions properly.
On Tuesday, floodwaters began to creep into West End in the heart of Brisbane, with police saying people who live or are near the Brisbane River should move to higher ground.
There had been no order as yet for mandatory evacuations in the suburb, police said.
Brisbane is expected to see further flooding overnight and into Wednesday, with the council warning about 200 properties could be flooded, most in the areas of Rocklea, Albion, Milton and Auchenflower.
Ms Bligh said modelling was being carried out to determine how the Toowoomba deluge would affect the situation in the capital.
Ms Bligh said it was clear the state was now mired in a very different sort of disaster.
"It is testing our emergency resources and it will test us as a community and as people," she said.
"It might be braking our hearts at the moment, but it will not break our will."
Four defence force helicopters have been sent to the flood zone along with extra swift-water rescue experts, Emergency Management Queensland told AAP.
More than 50 people remain holed up at a school in Grantham - a town that looks like a cyclone has swept through it, with houses and businesses destroyed and cars wedged in trees.
Meanwhile, the flood crisis continues to play out in other parts of the state.
Overnight, residents in Dalby and Chinchilla were evacuated for the second time in a fortnight.
There was also flooding in Gympie with the water moving down the Mary River towards Maryborough.
Ms Bligh and Mr Stewart repeated warnings for people to stay out of floodwaters.
"This water is deadly and it's not to be played with," the premier said.
- AAP