BRISBANE, Australia (AP) -- Greg Kowald was driving through the center of Toowoomba when a terrifying, tsunami-like wall of water roared through the streets of the northeast Australian city.

Office windows exploded, cars careened into trees and bobbed in the churning brown water like corks. The deluge washed away bridges and sidewalks; people desperately clung to power poles to survive. Before it was over, the flash flood left at least 10 dead and 78 missing.

"The water was literally leaping, six or 10 feet into the air, through creeks and over bridges and into parks," Kowald, a 53-year-old musician, told The Associated Press on Tuesday. "There was nowhere to escape, even if there had been warnings. There was just a sea of water about a kilometer (half a mile) wide."

The violent surge in Toowoomba brought the overall death toll from weeks of flooding in Queensland state to 20, a sudden acceleration in a crisis that had been unfolding gradually with swollen rivers overflowing their banks and inundating towns while moving toward the ocean. Queensland Premier Anna Bligh said there were "grave fears" for at least 18 of those missing.

The high waters headed next to Australia's third-largest city, Brisbane, where up to 9,000 homes were expected to be swamped. The Brisbane River overflowed its banks Tuesday and officials warned that dozens of low-lying neighborhoods and parts of downtown could be inundated in coming days.

But nothing downstream was expected to be as fierce as the flash flood that struck Toowoomba on Monday. It was sparked by a freak storm - up to 6 inches (150 millimeters) fell in half an hour.

"There was water coming down everywhere in biblical proportions," Toowoomba council member Joe Ramia told the AP.

Ramia, 63, was driving downtown when the flash flood struck. He parked his car and dashed on foot for higher ground, keeping an eye on the carnage unfolding below: Cars transformed into scrap metal as they were flung into an elevated railway line, giant metal industrial bins tossed about as if made of paper, a man clinging desperately to a power pole as the relentless tide surged around him.

Ramia watched as a rescue official pushed through the churning water and yanked the man to safety. Others, including five children, were not as lucky, and were swept to their deaths.

"You were powerless to do a thing," said Ramia, a lifelong resident of Toowoomba. "While we can rebuild, you can't replace people. ... I've never seen anything like this."

The raging water was strong enough to rip houses off their foundations. Leroy Shephard, who lives in the town of Grantham, east of Toowoomba, was inside his home when the flood struck.

"You could feel the whole house just pop up off its stumps, turn around, and go - for a 100 meters (330 feet) or something down my backyard," Shephard told Australian Broadcasting Corp.

He and his family spent five hours on the house's roof waiting for the waters to drop.

"It's not a good feeling having the floorboards under your feet just ripple, the whole house just ripple and crack, and watching rooms just disappear," he said.

Emergency services officers plucked more than 40 people from houses isolated overnight by the torrent that hit the Lockyer Valley, and thousands were being evacuated. In one small community in the path of the floodwaters, Forest Hill, the entire population of about 300 was being airlifted to safety in military helicopters, Bligh said.

Search and rescue efforts were hampered by more driving rain, though the bad weather was easing and Bligh said the search would get easier Wednesday.

Brisbane Mayor Campbell Newman said authorities were preparing for flooding affecting about 15,000 people in 80 suburbs.

The city is protected by a large dam built upstream after floods devastated downtown in 1974. But the reservoir was full, and officials had no choice but to release water that would cause low-level flooding in the city, Newman said. The alternative was a much worse torrent.

Steph Stewardson, a Brisbane graphic designer, said there was an exodus in a downtown area around lunchtime Tuesday when the river that goes through the city broke its banks. Stewardson, 40, hopped in her car and crossed the swollen river to collect her dog Boo from daycare while waters started covering the boardwalk stretching along its banks.

Stewardson took shelter in her house, and plans to stay there - for now.

"I'm about 800 meters (half a mile) from the river on a hill, so I think it's going to be OK," she told the AP.

Queensland has been in the grip of its worst flooding for more than two weeks, after tropical downpours covered an area the size of France and Germany combined. Entire towns have been swamped, more than 200,000 people affected, and the coal industry and farming have virtually shut down.

"The power of nature can still be a truly frightening power and we've seen that on display in this country," Prime Minister Julia Gillard said.

Police Commissioner Bob Atkinson described the events Monday as "an inland instant tsunami."

Forecasters said more flash floods could occur through the week.

Deputy Police Commissioner Ian Stewart said rescue efforts were concentrated on towns between Toowoomba and Brisbane, including hardest-hit Murphy's Creek and Grantham, where about 30 people sought shelter in a school isolated by the floodwaters.

The floods reached a second state Tuesday, with about 4,500 people stranded by high waters in bordering New South Wales, officials said, though the situation was not yet as dire as in Queensland.

Bligh said last week the cost of the floods could be as high as $5 billion, the latest figure available.

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Gelineau reported from Sydney. Tanalee Smith contributed to this report from Adelaide, Australia.