Rescuers raced on Tuesday to reach people trapped on roofs after a flash flood sent a massive wall of water through a valley in Australia's waterlogged east, tossing cars like toys, killing at least eight people and leaving 72 missing, officials said.

The sudden surge near the town of Toowoomba after a storm Monday lifted Australia's 2-week-old flood crisis in Queensland state to a new level and brought the overall death toll to 18.

Until then, the flooding had unfolded slowly as swollen rivers burst their banks and inundated towns while moving downstream toward the ocean.

Emergency services officers plucked more than 40 people from houses isolated overnight by the torrent that hit the Lockyer Valley on Monday, thunderstorms and more driving rain hampered efforts to send helicopters to help an unknown number of other people still in danger Tuesday.

Queensland state Premier Anna Bligh said four children were killed and there were "grave concerns" for at least 11 of the missing. Many of those still stranded or unaccounted for are families and young children, she said.

"This has been a night of extraordinary events," Bligh told reporters.

"We've seen acts of extreme bravery and courage from our emergency workers. We know they're out on the front line desperately trying to begin their search and rescue efforts, and we know we have people stranded and people lost."

She said the death toll stood at eight, but that "we expect that figure to rise and potentially quite dramatically."

Queensland has been in the grip of its worst flooding for more than two weeks, after tropical downpours across a vast area of the state covered an area the size of France and Germany combined.

Entire towns have been swamped, more than 200,000 people affected, and coal and farming industries virtually shut down.

Monday's flash flooding struck without warning in Toowoomba, a city of some 90,000 people nestled in mountains 2,300 feet (700 meters) above sea level. Bligh said an intense deluge fell over a concentrated area, sending a 26-foot (eight-meter), fast-moving torrent crashing through Toowoomba and smaller towns further down the valley.

On Tuesday, the water was still pushing its way downstream, flooding river systems as it moved toward the coast. Thousands were being evacuated from communities in the water's predicted path and residents in low-lying regions of the state capital of Brisbane — Australia's third-largest city — were urged to sandbag their homes.

"We have a grim and desperate situation," Bligh said. "This took everybody so unawares that there was no opportunity in most cases for people to get to safety."

Rescue workers were battling more bad weather Tuesday. Heavy rain and thunderstorms were forecast for the region for most of the day, which could lead to more flash flooding, the Bureau of Meteorology warned.

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

News video from late Monday showed houses submerged to the roof line in raging muddy waters, with people clambering on top. A man, woman and child sat on the roof of their car as waters churned around them with just inches (centimeters) to spare.

Among the dead were a mother and her two children whose car was swept away in the floodwaters, Bligh said. Two other children also were killed, she said.

In Toowoomba, the waters disappeared almost as fast as they arrived, leaving debris strewn throughout downtown and cars piled atop one another.

The flooding in recent weeks has cut roads and rail lines across Queensland, the state's coal industry has been virtually shut down, and cattle ranching and farming across a large part of the state are at a standstill.

Queensland officials have said the price of rebuilding homes, businesses and infrastructure, coupled with economic losses, could be as high as $5 billion.

On the other side of Australia, hot, dry conditions have sparked a wildfire that has destroyed at least four homes. Around 150 firefighters were battling a blaze about 70 miles (110 kilometers) south of the Western Australia state capital of Perth on Tuesday. There have been no reported injuries.