Latest: Hurricane Irma has moved inland near Naples which is expected to take the brunt of the category three storm.
The National Hurricane Centre says it's carrying winds of up to 115 miles per hour and that catastrophic storm surges are expected.
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The conditions have killed at least 27 people in the Caribbean and another three deaths have been confirmed in Florida.
Donald Trump says he will be travelling to the US state 'very soon but said right now lives are the priority.
"You do not want to be in that path. For the most part people have left but that is a bad path to be in."
Update 9.40pm: Hurricane Irma has been downgraded to a Category 3 storm - two down from the most severe level - as it moves north along Florida's West Coast.
But the US national hurricane centre is warning it will remain powerful.
Three people have died as winds of 130 miles per hour hit the Florida Keys earlier.
Emergency services in the area are concerned that water being drawn out from the coast due to Irma will return as a powerful storm surge later tonight and tomorrow.
Update 8pm: As Hurricane Irma heads away from Florida Keys there is growing concern that dangerous storm surges could soon hit the US state's West Coast.
So far three people have been killed in Florida with winds up to 130 miles an hour leaving more than a million homes and businesses without power.
Update 6.30pm: A British tourist caught in the path of Hurricane Irma has said he is "thankful to be here" after he was rescued by the US Air Force.
Alex Woolfall was on holiday on the Caribbean island of St Martin when the historic storm struck.
The PR consultant, from London, went on Twitter to post updates as winds battered the Westin Hotel, where he was sheltering in a concrete stairwell.
He wrote: "My God this noise! It's like standing behind a jet engine!! Constant booms & bangs. At least concrete stairwell not moving"
Mr Woolfall said he was airlifted to safety in Puerto Rico by a military plane as powerful Hurricane Jose was approaching.
"I am just tired but very thankful to be here," he told the Press Association after his rescue.
"I think probably all those on vacation would say it was a nightmare but it's over for us.
"What about the people of St Martin and the other islands? I just hope the aid and support they need comes."
Mr Woolfall described the devastation on the island after Irma hit.
"It's very badly damaged and it's heart-breaking to see people whose homes have been destroyed sitting outside in the street, especially when you see young children too."
Mr Woolfall said local hotel staff continued coming to work, despite the damage to their own property, while the manager worked tirelessly to arrange planes.
"I found that astonishing and very moving," he added.
Update 4.30pm: Officials in Florida think three reported deaths are due to Hurricane Irma - which has made landfall in the US State.
More than 6 million people were ordered to evacuate - with fears it could cause deadly storm surges.
Irma's already killed at least 22 people in the Caribbean.
Speaking to ABC's Good Morning America, Florida's governor Rick Scott made another appeal to residents to heed advice and prepare for a "devastating" storm surge as high as 15ft.
Update 4.10pm: As Hurricane Irma makes landfall on the US coast, police have confirmed a man's died after a pick-up truck smashed into a tree in Florida Keys.
They say it's the state's first casualty due to the Category 4 storm - which is whipping up winds of almost 210 kilometres per hour.
Six and a half million people were ordered to leave the state.
Update 3.30pm: Hurricane Irma's is battering the lower Florida Keys as a powerful category four storm with reports that over one million home shave now lost all power.
Irma lashed the area with maximum sustained winds near 130 mph and the US National Hurricane Centre said it was expected to remain a powerful storm as it moved through the Florida Keys and near the state's west coast.
This morning the hurricane was centred about 20 miles east-southeast of Key West, Florida, and was moving north-northwest at 8 mph.
The Key West International Airport measured sustained winds of 50 mph with a gust of up to 70 mph, according to the hurricane centre.
The National Weather Service issued tornado warnings for a wide swathe of Monroe, Miami-Dade and Broward counties in south Florida. The band of rain and tornado-producing cells was moving quickly, officials said. There were no immediate reports of tornadoes touching down.
Tens of thousands of people huddling in shelters watched for updates.
In the Tampa Bay area, access to all of Pinellas County's barrier islands, including the popular spring break destination of Clearwater Beach, was shut off.
The leading edge of the immense storm bent palm trees and spit rain across south Florida, knocking out power to hundreds of thousands of homes and businesses, as the eye approached Key West.
As the hurricane's eye approached the Florida Keys early Sunday, Carol Walterson Stroud, 60, and her family were huddled in a third floor apartment at a centre for the elderly in Key West.
"We are good so far," she said in a text message just before 5.30am. "It's blowing hard."
Mrs Stroud was with her husband, Tim Stroud, and granddaughter, Sierra Costello. Their dog Rocky was also riding out the storm.
Mrs Stroud said she planned to step outside once the eye of the hurricane passed over. She said she has stood in the eye of a hurricane before and it is "total peace and quiet".
Florida governor Rick Scott had warned residents in the state's evacuation zones on Saturday that "this is your last chance to make a good decision". About 6.4 million people were told to flee.
But because the storm is 350 to 400 miles wide, the entire Florida peninsula was exposed. Forecasters said the greater Miami area of six million people could still get life-threatening hurricane winds and storm surge of 4ft to 6ft.
Irma was at one time the most powerful hurricane ever recorded in the open Atlantic with a peak wind speed of 185 mph last week. It left more than 20 people dead across the Caribbean and as it moved north over the Gulf of Mexico's bathtub-warm water of nearly 90 degrees, it was expected to regain strength.
Meteorologists predicted Irma would plough into the Tampa Bay area Monday morning. The area has not been struck by a major hurricane since 1921, when its population was about 10,000, National Hurricane Centre spokesman Dennis Feltgen said. Now around three million people live there.
The latest course also still threatens Naples' mansion and yacht-lined canals, Sun City Centre's retirement homes, and Sanibel Island's shell-filled beaches.
Irma's course change caught many off guard and triggered a major round of last-minute evacuations in the Tampa area.
Many businesses had yet to protect windows with plywood or hurricane shutters. Some locals grumbled about the forecast, even though Florida's west coast had long been included in the zone of probability.
"For five days, we were told it was going to be on the east coast, and then 24 hours before it hits, we're now told it's coming up the west coast," said Jeff Beerbohm, 52, in St Petersburg. "As usual, the weatherman, I don't know why they're paid."
Nearly the entire Florida coastline remained under hurricane watches and warnings, and the latest projections could shift again, aiming the worst of the storm at other parts of the state.
Forecasters warned of storm surges as high as 15ft.
"This is going to sneak up on people," said Jamie Rhome, head of the hurricane centre's storm surge unit.
Given its mammoth size and strength and its course up the peninsula, it could prove one of the most devastating hurricanes ever to hit Florida, and inflict damage on a scale not seen there in 25 years.
Hurricane Andrew smashed into suburban Miami in 1992 with winds topping 165 mph, damaging or blowing apart more than 125,000 homes. At least 40 people died.
Update 10.02am: Hurricane Irma regained strength as it closed in on the Florida Keys early today, as forecasters monitored a crucial shift in its trajectory that could keep its ferocious eye off the southwest Florida coast and over warm gulf water.
The hurricane re-strengthened to category-four status with maximum sustained winds near 130 mph.
The US National Hurricane Centre said Irma was expected to gain a little more strength as it moved through the Straits of Florida and remain a powerful hurricane as it approached Florida.
Tens of thousands of people huddling in shelters watched for updates as the storm swung to the west, now potentially sparing Tampa as well as Miami the catastrophic head-on blow forecasters had been warning about for days.
But those few miles meant St Petersburg could get a direct hit, rather than its more populous twin across Tampa Bay. Neither city has suffered a major hurricane in nearly a century.
Hurricane Irma is closing in on the Florida Keys with top winds of 120mph as forecasters monitored a crucial shift in its trajectory that could keep its ferocious eye off the state's south-west coast and over warm gulf water.
Tens of thousands of people huddling in shelters watched for updates as the storm swung to the west, now potentially sparing Tampa as well Miami the catastrophic head-on blow forecasters had been warning about.
But those few miles meant St Petersburg could get a direct hit, rather than its more populous twin across Tampa Bay.
The leading edge of the immense storm bent palm trees and spit rain across South Florida, knocking out power to more than 170,000 homes and businesses, as the eye approached Key West.
If the centre of the storm keeps moving over warm Gulf of Mexico water, it may regain more strength before making landfall again.
St Petersburg, like Tampa, has not taken a head-on blow from a major hurricane in nearly a century.
Clearwater would be next, and then the storm would finally go inland north west of Ocala.
Irma currently has top sustained winds of 120mph and is moving northwards at about 6mph.
More than 170,000 homes and businesses in Florida have lost power and Florida Power and Light said more than half of those shutdowns were in the Miami-Dade area, where about 600,000 people have been ordered to evacuate.
The company has said it expects millions of people to lose power, with some areas experiencing prolonged outages.
The company said it has assembled the largest pre-storm workforce in US history, with more than 16,000 people ready to respond.