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Thousands of people are fleeing their homes and hospitals are being emptied as severe tropical cyclone Yasi bears down on the north Queensland coast.

Premier Anna Bligh says lives could be lost when Yasi, expected to be more devastating that Cyclone Larry, makes landfall somewhere between Cairns and Innisfail.

The category three storm is expected to dramatically intensify before hitting the coast as a severe category four about 1am AEST (3am NZT) on Thursday, with winds in excess of 250km/h.

Much of the north Queensland coast is also braced for a dangerous storm surge, a threat that has already forced many to flee low-lying homes.

Ms Bligh said the air force would fly 250 patients from the waterfront Cairns Base and Cairns Private hospitals to safety in Brisbane on Tuesday evening.

Brisbane's hospitals are on "code brown" alert to deal with the influx, meaning some elective surgery will be cancelled.

Defence force aircraft are being fitted out for the special medical flights.

Residents in waterfront and low-lying areas around Cairns and Townsville are leaving their homes as Yasi advances, but so far there have been no mandatory evacuations.

Ms Bligh said Yasi's winds would be "life-threatening" but associated flooding would be more dangerous.

" ... in serious cyclone events around the world, more people are injured or lose their lives in the water that is associated with storm surge than in wind and flying debris," she told reporters in Brisbane on Tuesday afternoon.

"Loss of life and serious injury ultimately will depend in some respects on people being sensible, listening to warnings, taking advice and not treating this as a tourist event.

"It will be a display of the awesome power of nature but it's not something you want to go outside and watch."

People in low-lying properties in a massive danger zone that stretches from Innisfail to Mackay have been advised to get to higher ground on Tuesday.

State disaster co-ordinator Ian Stewart has warned people not to drive in the high winds expected on Wednesday morning, and has asked them to get as far south as possible, as safely as possible.

"In reality, we would like people to get as far south as possible, as quickly as possible, without of course breaking the rules," he told reporters.

"Mackay is probably a target area for ... complete safety."

Queensland chief medical officer Jeannette Young said the evacuated patients included people in intensive care, pregnant women, premature babies and dialysis patients.

"We do this every single day in Queensland, we have a very big state and we move patients around the state all the time," she said.

"We'll be putting our doctors and nurses on those planes to move those patients safely."

Airlines have put on extra flights to help visitors leave the area before the cyclone, with Townsville airport set to close on Tuesday night and Cairns possibly on Wednesday morning.

Schools in Townsville and further north will be closed from Wednesday and sea ports are also closed.