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A weather satellite image shows Cyclone Yasi passing near the Solomon Islands and Vanuatu heading toward the coast of Australia on Monday. ((NOAA/Reuters))

A powerful cyclone closing in on Australia's northeast threatens to bring torrential rain and huge storm surges to regions already saturated by flooding.

Queensland Premier Anna Bligh is warning residents that Cyclone Yasi could be the biggest the state has ever faced.

The cyclone strengthened to a Category 3 storm on Monday with winds up to 185 km/h, and is expected to strike the Queensland coast on Wednesday or Thursday as a Category 4 storm with gusts up to 260 km/h.

Extremely heavy rain could fall in areas still reeling from previous flooding, warned Bligh.

"We can expect very significant rainfall, in some cases up to a metre, into catchments that are already saturated.

"We are currently doing modelling into what that might mean, particularly into areas such as the central and western areas of Queensland.… which we have already seen significant flooding in."

Evacuations begin

Residents in vulnerable zones and low-lying areas have been told to move to higher ground.

"Cyclones can at the last minute turn off the coast, and I certainly hope this one does," said Bligh.

"But the bureau advises me in the most serious terms, that all of the modelling right now says this is going to cross our coast."

Deputy police commissioner Ian Stewart said residents should be prepared with flashlights, food and water. "This is a very, very serious threat to the safety of our coastline and the safety of our community."

Queensland has suffered months of flooding since heavy rains struck in November.

The floodwaters killed 35 people, damaged or destroyed 30,000 homes and businesses, and left parts of Brisbane, the country's third-largest city and the state capital, under water for days.

With files from the Australian Broadcasting Corporation and The Associated Press