Ian now a Category 4 hurricane as it approaches southwestern Florida

Hurricane Ian rapidly intensified off Florida's southwest coast Wednesday morning, gaining top winds of 250 kilometres per hour, just shy of the most dangerous Category 5 status. Damaging winds and rain lashed the state's heavily populated Gulf Coast, with the Naples to Sarasota regions at "highest risk" of a devastating storm surge.

U.S. air force hurricane hunters confirmed Ian gained strength over warm Gulf of Mexico waters after battering Cuba, where island residents were left without power.

The. U.S. National Hurricane Center in Miami said Ian was centred about 100 kilometres west-southwest of Naples at 7 a.m. ET, swirling toward the coast at 17 kilometres per hour. Meteorologists and the Federal Emergency Management Administration have said that speed could slow as it nears landfall in Florida, meaning the storm could linger before it passes through.

"This is going to be a nasty, nasty day, two days," Florida Gov. Ron DeSantis said early Wednesday. "This is going to be a rough stretch."

The major hurricane has prompted warnings of possibly dangerous storm surge along the state's heavily populated Gulf Coast from Bonita Beach to the Tampa Bay region.

The precise location of landfall was still uncertain, but with Ian's tropical storm-force winds extending 280 kilometres from its centre, flash floods were possible across the whole state. Isolated tornadoes were spinning off the storm well ahead of landfall, one of which damaged small planes and a hangar at the North Perry Airport, west of Hollywood along the Atlantic coast.

The most damaging winds could hit a rapidly developing coastline where the population has jumped sevenfold since 1970, according to the U.S. census, which shows Lee County has seen the eighth-largest population growth among more than 180 Atlantic and Gulf coast counties in the past 50 years.

There were 250,000 people in the Fort Myers/Lee County mandatory evacuation zones, and authorities worried ahead of the storm how many would leave.

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

Floridians rushed to board up their homes, stash precious belongings on upper floors and flee.

"You can't do anything about natural disasters," said Vinod Nair, who drove inland from the Tampa area Tuesday with his wife, son, dog and two kittens seeking a hotel in the tourist district of Orlando. "We live in a high-risk zone, so we thought it best to evacuate."

Nair and his family were among at least 2.5 million Florida residents ordered to evacuate in anticipation of a powerful storm surge, high winds and flooding rains.

Power outages anticipated

Florida Power and Light warned those in Ian's path to brace for days without electricity. As a precaution, hundreds of residents were being evacuated from several nursing homes in the Tampa area, where hospitals also were moving some patients.

Winds exceeding tropical-storm strength of 63 km/h reached Florida by 3 a.m., and hurricane-force winds were recorded in Florida by 6 a.m., well in advance of the storm's eyewall moving inland, the Miami-based centre said.

Forecasters said the storm surge could reach 3.6 metres if it peaks at high tide. Rainfall near the area of landfall could top 46 centimetres.

Airports in Tampa, St. Petersburg and Key West closed. Disney World theme parks and Sea World in Orlando all closed ahead of the storm.

A couple from England on vacation in Tampa found themselves faced with riding out the storm at a shelter. Glyn and Christine Williams of London were told to leave their hotel near the beach when evacuations were ordered. Because the airport shut down, they could get no flight home.

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"Unfortunately, all the hotels are full or closed, so it looks as though we're going to be in one of the shelters," Christine Williams said.

"You know, you got to go with the flow," Glyn Williams added. "So we're quite happy doing what we're doing."

Georgia, South Carolina also on alert

Parts of Georgia and South Carolina also could see flooding rains and some coastal surge into Saturday. Georgia Gov. Brian Kemp pre-emptively declared an emergency, putting 500 National Guard troops on standby to respond as needed.

Before turning toward Florida, Ian struck Cuba's Pinar del Rio province with sustained winds of 205 km/h, causing destruction in the island nation's world-famous tobacco belt.

Local government station TelePinar reported heavy damage at the main hospital in Pinar del Rio city, tweeting photos of collapsed ceilings, widely flung debris and toppled trees. No deaths were reported. 

Ian's winds damaged one of Cuba's most important tobacco farms, Finca Robaina.

"It was apocalyptic, a real disaster," said Hirochi Robaina, owner of the farm that bears his name and that his grandfather made known internationally.

Authorities were working overnight to gradually restore service to the country's 11 million people, according to a statement from Cuba's Electric Union.