Hurricane Ian has left a path of destruction in south-west Florida, trapping people in flooded homes, cutting off a bridge to a barrier island and knocking out power to 2.5 million people as it dumped rain across the peninsula.

One of the strongest hurricanes to ever hit the United States threatened catastrophic flooding around the state.

Ian’s tropical-storm-force winds extended outward up to 665 kilometre, drenching much of Florida and the southeastern Atlantic coast.

Authorities confirmed at least one storm death in Florida.

A 72-year-old man was found dead early on Thursday in water in a canal behind his home in Deltona near Daytona Beach, the Volusia County Sheriff’s Office said in a statement.

It said he appeared to be using a hose to drain his pool into the wide canal and fell down an incline that was “extremely soft and slippery due to the heavy rain.”

Another Florida sheriff said he believed the death toll would be “in the hundreds”.

Lee County Sheriff Carmine Marceno told ABC’s Good Morning America that his office was receiving thousands of 911 calls from people needing rescue in the county that includes Fort Myers, but roadways were still impassable and bridges are compromised.

“It crushed us,” Sheriff Marceno said. “We still cannot access many of the people that are in need.”

Fort Myers Mayor Kevin Anderson told NBC’s Today that he had not been told of any deaths in the city.

Emergency crews sawed through toppled trees to reach people in flooded homes, but with no electricity and virtually no mobile phone service, it was impossible for many people to call for help.

The National Hurricane Centre said Ian became a tropical storm over land early Thursday and was expected to regain near-hurricane strength after emerging over Atlantic waters near the Kennedy Space Centre later in the day, with South Carolina in its sights for a second US landfall.

A stretch of the Gulf Coast remained inundated by ocean water, pushed ashore by the massive storm.

A chunk of the Sanibel Causeway fell into the sea, cutting off access to the barrier island where 6300 people normally live.

In Port Charlotte, the storm surge flooded a hospital’s emergency room even as fierce winds ripped away part of the roof from its intensive care unit, according to a doctor who works there.

Water gushed down onto the ICU, forcing them to evacuate their sickest patients – some on ventilators – to other floors, said Dr Birgit Bodine of HCA Florida Fawcett Hospital.

The Florida Highway Patrol shut down a section of the Florida Turnpike, main artery in the middle of the state, in the Orlando area due to significant flooding and said it will remain closed until the water subsides.

Ian’s strength at landfall was Category 4, tying it for the fifth-strongest hurricane, when measured by wind speed, ever to strike the US.

A boat carrying Cuban migrants sank on Wednesday in stormy weather east of Key West.

The US Coast Guard initiated a search and rescue mission for 23 people and managed to find three survivors south of the Florida Keys, officials said.

Four other Cubans swam to Stock Island, just east of Key West, the US Border Patrol said. Air crews continued to search for possibly 20 remaining migrants.

The storm previously tore into Cuba, killing two people and bringing down the country’s electrical grid.

More than 2.5 million Florida homes and businesses were left without electricity, according to the PowerOutage.us site.

-AP