Cyclone Yasi is expected to be larger and more intense than 2006's devastating Cyclone Larry when it slams into the north Queensland coast some time tomorrow night.

Queensland Premier Anna Bligh delivered the stark assessment as she warned residents that today was their last chance to abandon homes in low-lying suburbs in the path of the possible high category four system.

The cyclone is expected to pack winds of up to 280 kilometres per hour when it hits the coast and makes landfall near Cairns at about 1:00am AEST on Thursday.

A cyclone warning has been declared for coastal areas from Cooktown to Sarina.

"This is not only now tracking as more intense than Cyclone Larry, it is significantly larger than Cyclone Larry," Ms Bligh told a press conference today.

'Life-threatening'

Ms Bligh says communities need to be prepared to be without food and power for an extended period of time.

"This storm is huge and it is life-threatening," she said.

"Being well prepared is our best defence.

"I know many of us will feel that Queensland has already borne about much as we can bear when it comes to disasters and storms, but more is being asked of us.

"I am confident that we are able to rise to this next challenge."

Ms Bligh says the storm has the potential to be the biggest the state has ever seen.

She said the storm's eye could take more than an hour to pass and warned that the strongest winds would hit after the eye had passed.

"This eye could last for more than an hour and at the end of that period the next thing that will be felt is the strongest possible winds," she said.

The storm could still be category three when it hits the Atherton Tablelands, and category two at Mackay.

A cyclone watch has been declared for coastal areas from Lockhart River to Cooktown and Sarina to Yeppoon and for southern Cape York Peninsula and inland areas north of Charters Towers.

Evacuations

Deputy Police Commissioner Ian Stewart says mandatory evacuation orders will be issued today for those living in low-lying coastal areas that may be affected by storm surges and flash flooding.

"Please make no mistake - this storm is a deadly event," he said.

"People need to take action between now and tomorrow morning, after which time in the high impact areas it will be unsafe to travel.

"Do not make any mistake, do not be undecided - take action now."

Residents in low-lying waterfront areas from Innisfail to Mackay are being warned that today will be their last chance to get out ahead of the storm's impact.

"We are very concerned about storm surges causing serious powerful flash flooding," Ms Bligh said.

"Every council has identified those houses most at risk and if you are in one of those areas, you should be relocating yourself and your family today.

"That means whole suburbs in some parts of the region will be looking for alternative accommodation with friends and family today.

"Today is the last opportunity that people will have to make all the preparations they need to keep themselves and their families safe.

"That means that if you are in a low-lying waterfront area, you should be thinking of relocating your family to a friend in a higher place today."

EMQ spokesman Bruce Grady from says residents who do not know if they should evacuate can contact their local council.

"People in low-lying areas need to be making plans now to relocate and maybe during the course of today there will be a mandatory evacuation order given," he said.

Emergency Management Queensland (EMQ) says houses in low-lying areas of Cairns will be evacuated today as the threat of a huge storm surge looms.

EMQ area director Wayne Hepple says communities at Innisfail are at risk of flooding as well as the Cairns suburbs of Manoora, Manunda and Mooroobool.

"The storm surge will be an event that occurs on the southern side of the cyclone, so from the eye to the south," he said.

"It's just the nature of the winds and how it pushes it up onto the coast.

"If you are on that southern side, that's why this thing is going to be quite dangerous."

Cyclone to intensify

Forecaster Ben Suter says it is still a category three cyclone, but will intensify as a high category four system when it makes landfall, with winds reaching up to 280 kilometres an hour.

"We have strong gale force winds extending just north of Cooktown and all the way down to Bowen," he said.

"It looks like making landfall on the current forecast somewhere between Cairns and Innisfail and it does still look to be a high category four when it does so.

"The current crossing looks earlier as well, maybe around midnight [AEST] Wednesday, going into Thursday."

Mr Suter says the cyclone will cause a storm surge.

"The worst of any storm surge will probably be Innisfail southwards, particularly around Townsville, even though the charts are further north," he said.

"I think even Townsville could see a fairly storm surge.

"If this forecast track does actually go a bit further north, then obviously that storm surge risk will transfer northwards."

Maritime Safety Queensland (MSQ) has issued a yellow alert for all boats from Cape Flattery in Cape York to Mourilyan, south of Innisfail, out of the water.

All ports from Cairns to Mackay will be closed from late today.

Police in Cairns are urging people to be prepared with torches, radios, basic first aid supplies and a supply of food.

Cyclone plan

Townsville Mayor Les Tyrell says authorities will evacuate retirement and nursing homes along the seaside suburb of Pallarenda today.

He says the size of Yasi means even if it does cross north of Townsville, the city may still be affected by destructive winds and floods.

Emergency authorities in Mackay say residents need to have a plan in place well before the strong winds start affecting the region.

Inspector Peter Flanders says people must make sure they have a plan for their families.

"If you're staying in your house, make sure that every person in your family knows what the plan is, they know where to go in the house should a cyclone hit," he said.

"If you are thinking about moving your family do it early - the whole key is preparation.

"If the cyclone does hit with significant impact, all of those things need to be in place - it's too late once the wind starts blowing."

Mackay Mayor Col Meng says a tidal surge is a concern.

"Wednesday is a 5.7 metre tide, so we have a reasonably high tide and if we have the river in flood as well and a 5 metre tide and get a surge on top of that, that's when our trouble will be," he said.

"The serious thing is everything's saturated - we already do have those flood conditions.

"Our worry is if we do get that tidal surge it will push back in, they're saying it could be up to four metres."

Whitsunday Regional Mayor Mike Brunker says tourists in the area should postpone their holiday and move south of Rockhampton.

"If you've got friends in Brisbane, go to Brisbane," he said.

"If you're on holidays and you live in Brisbane or Melbourne or whatever - I'd be relocating, redoing your plans - there's not going to be a holiday experience here for you."

Councils ready

Local Government Association of Queensland (LGAQ) president Greg Hallam says councils are ready to deal with Cyclone Yasi.

"Councils have made sure that they've identified evacuation routes," he said.

"They've looked at low-lying areas that could be inundated, they've moved council assets, they're cooperating with the police, communicating to the local community, mobilising all of their equipment to assist in any emergency situation."

Mr Hallam says there should not be any problems with getting food supplies to affected areas.

The Local Disaster Management Group also met in Cairns yesterday to discuss preparations.

Cairns Mayor Val Schier, who chairs the local group, says it will keep monitoring the system as it approaches the coast.

"It will impact on Cairns, even though we're on the fringe of it," she said.

"We still may get winds of up to 100 kilometres an hour by Wednesday afternoon, so we need to make sure that people are able to respond to that.

"What we're saying to people is that they need to make sure their preparations are complete."

- Reporting by Kirsty Sexton-McGrath, Maria Hatzakis, Penny Timms, Melissa Maddison, Sigrid Brown, Brad Ryan and Imogen Brennan