One of the strongest hurricanes to ever hit the United States has barrelled across the Florida peninsula, threatening catastrophic flooding inland.

Hurricane Ian turned streets into rivers and blew down trees as it slammed into southwest Florida.
Hurricane Ian turned streets into rivers and blew down trees as it slammed into southwest Florida. (AP)

Hurricane Ian has left a path of destruction in southwest Florida, trapping people in flooded homes, damaging the roof of a hospital intensive care unit and knocking out power to two million people before aiming for the Atlantic Coast.

One of the strongest hurricanes to ever hit the United States barrelled across the Florida peninsula overnight Wednesday, threatening catastrophic flooding inland, the National Hurricane Centre warned.

The centre said Ian became a tropical storm over land early Thursday and was expected to emerge over Atlantic waters near the Kennedy Space Centre later in the day.

Flooding rains continued across the state, and a stretch of the Gulf Coast remained inundated by ocean water, pushed ashore by the massive storm.

“Severe and life-threatening storm surge inundation of 8 to 10 feet above ground level along with destructive waves is ongoing along the southwest Florida coastline from Englewood to Bonita Beach, including Charlotte Harbor,” the centre said.

In Port Charlotte, along Florida's Gulf Coast, the storm surge flooded a lower-level emergency room in a hospital even as fierce winds ripped away part of the roof from its intensive care unit, according to a doctor who works there.

Law enforcement officials in nearby Fort Myers received calls from people trapped in flooded homes or from worried relatives. Pleas were also posted on social media sites, some with video showing debris-covered water sloshing toward homes’ eaves.

READ MORE: Hurricane Ian slams Florida as Category 4 fury

Streets turned into rivers

Hurricane Ian turned streets into rivers and blew down trees as it slammed into southwest Florida on Wednesday with 150 mph (241 kph) winds, pushing a wall of storm surge.

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

Ian dropped to a tropical storm early Thursday over land, but was expected to intensify again once its centre moves over the Atlantic Ocean and menace the South Carolina coast Friday at near-hurricane strength.

Storm surges as high as 6 feet (2 meters) were expected on both sides of the peninsula.

At 5 am Thursday, the storm was about 40 miles (70 km) southeast of Orlando and 35 miles (55 kilometres) southwest of Cape Canaveral, carrying maximum sustained winds of 65 mph (100 kph) and moving toward the cape at 8 mph (13 kmh), the Miami-based hurricane centre said.

Hurricane warnings were lowered to tropical storm warnings across the Florida peninsula, with widespread, catastrophic flooding remaining likely, the hurricane centre said.

No deaths were reported in the United States from Ian by late Wednesday. But a boat carrying Cuban migrants sank 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 about two miles (three kilometres) 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.

READ MORE: Millions urged to evacuate as Hurricane Ian draws near Florida

Source: AP