FORT MYERS (Florida) • Millions of people huddled in shelters or in battened-down homes in Florida yesterday morning as Hurricane Irma, one of the most powerful storms ever recorded in the Atlantic, hit the state with 210kmh winds.

The National Hurricane Centre (NHC) forecast potentially deadly storm surges - water driven ashore by the winds - of up to 4.6m along some parts of the coast.

As the storm made landfall on the Florida Keys archipelago off the tip of southern Florida, torrential rain and lashing winds knocked out power to more than one million customers on the mainland, said utility officials.

"Pray for us," Florida Governor Rick Scott said in an ABC News interview as his state braced itself for the massive storm, which has already left a trail of destruction through the Caribbean.

Irma, which regained Category 4 strength early yesterday, prompted one of the largest evacuations in United States history. It is expected to cause billions of dollars in damage to the third-most populous US state, a major tourism hub with an economy comprising about 5 per cent of US gross domestic product.

A day after hitting Cuba's northern coast, Irma was on a path that would take it along Florida's Gulf of Mexico coast, near population centres including Tampa and St Petersburg, the NHC said. Hundreds of thousands of people spent the night in emergency shelters.

The hurricane, which killed at least 25 people as it tore through the Caribbean islands last week, has already claimed at least one life in Florida. Emergency responders in the Florida Keys said they pulled a man's body from his pickup truck, which had crashed into a tree in high winds. But officials say it is the water and not the winds that people should fear most.

"Storm surge has the highest potential to kill the most amount of people and to cause the most amount of damage," Mr Brock Long, administrator of the Federal Emergency Management Agency, told Fox News Sunday.

One woman in Miami's Little Haiti neighbourhood delivered her own baby, with medical personnel coaching her on the phone because emergency responders were not able to reach her, the city of Miami said on Twitter. The two are now at the hospital, it said.

The NHC has put out a hurricane warning and a tropical storm warning stretching across almost all of Florida into Georgia and South Carolina - an area where more than 20 million people live.

Irma comes just days after Hurricane Harvey dumped record-setting rain in Texas, causing unprecedented flooding, killing at least 60 people and leaving an estimated US$180 billion (S$241.5 billion) in property damage in its wake.

On Saturday, Irma battered central Cuba, knocking down power lines, uprooting trees and ripping the roofs off homes as it headed towards Florida.

The Cuban authorities said they had evacuated more than a million people as a precaution, including about 4,000 in the capital.

It was the first time the eye of a Category 5 storm had made landfall in Cuba since 1932, state media said.

On Florida's west coast, resident Charley Ball, 62, said he expected a storm surge to completely engulf the island of Sanibel where he lives.

"Just left the island and said goodbye to everything I own," he said.

REUTERS, AGENCE FRANCE-PRESSE