Canberra - A powerful cyclone hit Australia's far northeast early on Monday near the tropical city of Cairns, with winds of up to 290km/h uprooting trees, flattening crops and ripping off the roofs of houses.

Tropical Cyclone Larry posed a "very serious threat to life and property" in the far north of Queensland state, the Australian Bureau of Meteorology said, adding it had forced thousands of people to take shelter or evacuate.

Prime Minister John Howard ordered military helicopters on alert for rescue operations, but officials said the cyclone was downgraded to a category 4 from a category 5 storm as it came ashore near the town of Innisfail.

"It still poses a real threat to people and property," Bruce Gunn from Australia's Cyclone Warning Centre told Sky television, adding that flying debris was the greatest danger to people.

"A large number of houses have been unroofed," Queensland police superintendent Mike Keating told the Seven television network. He said there were reports of people suffering minor injuries, although the number was small, at this stage.

Steven Russo from the township of Wangan told the Seven network he hid under his bed with his two children and said the scene outside was "absolute devastation - you can't describe it".

Cairns is the main tourist centre of north Queensland and is a base for visitors to the Great Barrier Reef and inland tropical rainforests. The area is also home to about 25% of Australia's sugar crop and most of Australia's banana industry.

Local council deputy mayor George Pervan told AustralianAssociated press the cyclone had torn through the sugar cane and banana crops, causing widespread damage.

There were no reports of any damage to Australia's offshore oil and gas fields, which are located off the west coast, officials said. But mining operations further inland were bracing for high winds as the storm moved west.

Kim Robinson, the managing director of Kagara Zinc Ltd said the firm's ore treatment plant had been evacuated, but he did not expect any lasting damage to the facility, which is located well inland from Cairns.

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