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 forecast to reach up to 300km/h (190mph) Cyclone Yasi is ripping roofs off buildings and has cut power to at least 90,000 people.
The destructive core hit south of Cairns, with forecasters warning of substantial damage and likely deaths.
Queensland's premier has warned of devastation on an unprecedented scale.
Anna Bligh described the weather system as the "most catastrophic storm ever seen" in the state, and it has been classed as a "Category Five" typhoon - the highest grade in the scale used to measure such storms.
She warned that it could cause a tidal surge as high as nine metres (nearly 30ft), overwhelming low-lying coastal areas.
She said it would be a difficult night and a tough few days for the people of north Queensland, adding: "We are in completely uncharted waters."
Prime Minister Julia Gillard described the storm as a "cyclone of savagery and intensity".
"People are facing some really dreadful hours in front of them," she said.
The state disaster co-ordinator warned residents they would be on their own for up to 24 hours.
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 the state's history, triggered by tropical storms which have battered the region since the end of November.