Anna Burns-Francis: US correspondent as Hurricane Ian hits Florida - Early Edition on Newstalk ZB

Hurricane Ian's most damaging winds have begun hitting Florida's southwest coast, lashing the state with heavy rain and pushing a devastating storm surge after strengthening to the threshold of the most dangerous Category 5 status.

Fueled by warm waters in the Gulf of Mexico, Ian grew to a catastrophic Category 4 hurricane overnight with top winds of 250km/h, according to the National Hurricane Center.

The storm trudged on a track that would have it making landfall north of the heavily populated Fort Myers area, which forecasters said could be inundated by a storm surge of up to 5.5m.

People walk where water is receding out of Tampa Bay due to a negative surge ahead of Hurricane Ian. Photo / Steve Helber, AP

"This is going to be a nasty nasty day, two days," Florida Gov. Ron DeSantis said, stressing that people in Ian's path along the coast should rush to the safest possible shelter and stay there.

Ian menaced Florida after bringing destruction Tuesday to western Cuba, where two people were reported dead and the storm brought down the country's electricity grid.

A classic American car drives past utility poles tilted by Hurricane Ian in Pinar del Rio, Cuba. Photo / Ramon Espinosa, AP

Ian's centre was about 80km west of Naples at noon Wednesday, as it churned toward the coast at 15km/h. Ian's plodding pace meant the storm was expected to spend a day or more crawling across the Florida peninsula, dumping flooding rains of 300-450mm across a broad area including Tampa, Orlando and Jacksonville in the state's northeast corner.

Catastrophic storm surges could push 3.6m of water or more across more than 400km of coastline, from Bonita Beach to Englewood, the hurricane centre warned.

"It's going to get a lot worse very quickly. So please hunker down," DeSantis said.

Ivan Mendoza begins to repair damage at his mobile home in Davie, Florida, as Hurricane Ian rapidly intensified. Photo / Joe Cavaretta, South Florida Sun-Sentinel via AP

Off the coast on Sanibel Island near Fort Myers, swirling water-covered residential streets and was halfway up mailbox posts by mid-morning. Seawater rushed out of Tampa Bay, leaving parts of the muddy bottom exposed, and waves crashed over the end of a wooden pier at Naples.

More than 2.5 million people were under mandatory evacuation orders but, by law, no one could be forced to flee. The governor said the state has 30,000 linemen, urban search and rescue teams, and 7000 National Guard troops from Florida and elsewhere ready to help once the weather clears.

Florida residents rushed ahead of the impact to board up their homes, stash precious belongings on upper floors and join long lines of cars leaving the shore.

Utility trucks are staged in a rural lot in The Villages of Sumter County, Florida, in readiness for Hurricane Ian. Photo / Stephen M. Dowell, Orlando Sentinel via AP

Some chose to stay and ride out the storm. Jared Lewis, a Tampa delivery driver, said his home has withstood hurricanes in the past, though not as powerful as Ian.

"It is kind of scary, makes you a bit anxious," Lewis said. "After the last year of not having any, now you go to a Category 4 or 5. We are more used to the 2s and 3s."

Forecasters predicted Ian would make landfall more than 160km south of Tampa and St. Petersberg, likely sparing the densely populated Tampa Bay area from its first direct hit by a major hurricane since 1921.

An airplane overturned by a likely tornado produced by the outer bands of Hurricane Ian at North Perry Airport in Pembroke Pines. Photo / Wilfredo Lee, AP

Officials warned residents that Tampa could still experience powerful winds and up to 500mm of rain.

"Please, please, please be aware that we are not out of danger yet," Tampa Mayor Jane Castor said in a video on Twitter. "Flooding is still going to occur."

During the night, Ian went through a natural cycle when it lost its old eye and formed a new one. The timing was bad for the Florida coast, because the storm got stronger and larger — 193km/h to 250km/h — with landfall just a few hours away.

The size of the storm also grew, with tropical storm force winds extending 280km from the hurricane's centre.

"With the higher intensity you're going to see more extensive wind damage," University of Miami hurricane researcher Brian McNoldy said. "The larger wind field means that more people will experience those storm-force winds."

The most damaging winds could hit a coastline where the population has jumped sevenfold since 1970, according to the US Census.

Vinod Nair wasn't taking any chances. He drove inland from the Tampa area Tuesday with his wife, son, dog and two kittens to a hotel in Orlando, w