Fierce winds and driving rains brought by the most powerful storm ever to hit Queensland are lashing northern coastal areas of the Australian state.
With winds reaching up to 290km/h (181mph), Cyclone Yasi is ripping roofs off buildings and has cut power to at least 100,000 people.
The storm struck south of Cairns and is moving inland, with forecasters warning of severe damage and likely deaths.
Queensland's premier has warned of devastation on an unprecedented scale.
The town of Tully, close to where the cyclone hit land, is a "scene of mass devastation", resident Ross Sorbello told the Sydney Morning Herald.
Mr Sorbello, who briefly went outside as the eye of the storm passed over, said roofs were ripped from houses, electricity poles were down and the streets were covered with debris.
Tully resident Stephanie Grimaz said that houses in her street had been torn apart, the Queensland Times reported.
"The flat from across the street is in our front yard and we can see other houses which have just been destroyed," she said.
Other residents of Tully described tree tops being shredded by winds that roared like jet engines, and water being forced under doors by the pressure.
The nearby communities of Mission Beach and Innisfail are also believed to be badly affected.
Officials say the full extent of the damage will not be known until daybreak.
More than 10,000 people are in evacuation centres, which became so overcrowded that people were turned away.
Yasi was classed as a category five cyclone as it crossed the coast - the highest grade in the scale used to measure such storms. The Australian Bureau of Meteorology later downgraded the storm to category four and then to category three, but still classified it as dangerous.
State Premier Anna Bligh described the weather system as the "most catastrophic storm ever seen" in the state.
She warned that it could cause a tidal surge as high as 9m (nearly 30ft) in some places, overwhelming low-lying coastal areas.
"It will take all of us and all of our strength to overcome this. The next 24 hours I think are going to be very, very tough ones for everybody," she told a news briefing.
Prime Minister Julia Gillard described the storm as a "cyclone of savagery and intensity".
The state disaster co-ordinator, Ian Stewart, warned residents they would be on their own during the coming hours as it was too dangerous to send out emergency workers.
Many fear that Yasi could be worse than Cyclone Tracy, which hit Darwin on Christmas Eve in 1974 and killed 71 people. That was a category four storm.
The cyclone follows the worst floods in Queensland's history, triggered by tropical storms which have battered the region since the end of November.
Cyclone Yasi made landfall between Innisfail and Cardwell at around midnight local time (1400 GMT Wednesday).
The eye of the storm was reported to be 35km (22 miles) in width, with a front stretching across 650km (400 miles).
Mr Stewart told Australian television that deaths were "very likely" and there would be "significant destruction of buildings".
A resident of Ravenshoe, west of Innisfail, who gave her name only as Glenda, says she is on an isolated property.
"We couldn't get any tape for our windows so we tried to use wide sticky tape but it's peeling off... we are very scared. One side of our whole house is just glass," she told ABC News.
"We are actually camping under a desk that is bolted to concrete walls on two sides."
Those remaining in their homes were told to tape up windows, fill sandbags and prepare a "safe room" with mattresses, pillows, a radio, food and water supplies to wait out the cyclone.
They were also encouraged to fill bathtubs with water for drinking supplies.
Cairns resident Philip Baker told the BBC it seemed "a safer bet" to stay in his home rather than flee or head to an overcrowded evacuation centre with his wife and young daughter.
"We're as prepared as we can be. There is little left to do but wait.
"The authorities have been wonderful, supplying us with updates and the latest information via text. We've been told that we might lose power and the phone lines in the next few hours.
"The windows have been taped and if the situation rapidly deteriorates we plan to bunker down in a windowless room when the storm hits - there's just enough room to fit a single blow-up mattress on the floor. We're reasonably high up, so hopefully should be okay."
More than 400,000 people live in the cyclone's path. The area, which includes the Great Barrier Reef, is also popular with tourists.
Cairns airport closed on Wednesday. Rail lines, mines and coal ports have also shut down.
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