Irma weakens, but remains lethal as it sweeps past Florida

Hurricane Irma weakened into a tropical depression late on Monday, but remained deadly as it swirled beyond Florida, killing at least three people in Georgia, flooding the coast, sending trees crashing onto homes and forcing the world's busiest airport in Atlanta to cancel hundreds of flights.

Most of Florida spent Monday night in sweltering darkness after the diminished but still powerful Irma downed power lines and flooded the last dry corner of the state before wreaking havoc across Georgia and South Carolina.

By this morning, more than 13 million people, or two-thirds of Florida's population, were without power, according to the State Emergency Response Team, after rains and storm surge flooded Jacksonville in the state's north-eastern corner.

After leaving Florida as a tropical storm, Irma killed three people in Georgia and one in South Carolina, before being downgraded to a tropical depression over Columbus, Ga on Monday night.

An aircraft carrier and other Navy ships were headed to the Florida Keys, low-lying islands hit especially hard when Irma, then a Category 4 hurricane, struck on Sunday.

The former hurricane remained an immense, 668 km wide storm as its centre moved on from Florida Monday afternoon, giving its still-formidable gusts and drenching rains a far reach.

''I just hope everyone survived,'' Gov Rick Scott of Florida said on Monday after completing a flyover of the islands.

Some 5,40,000 people were ordered to evacuate days earlier from Savannah and the rest of Georgia's coast. Irma sent 4 feet of ocean water into downtown Charleston, South Carolina, as the storm's centre passed 400 km away. City officials urged residents to stay off the streets as almost 1 metre of water above dry ground is expected overnight.

Over the next two days, Irma is expected to push into Alabama, Mississippi and Tennessee.

At least 42 people have died as a result of the storm, including at least eight in the continental United States, according to The Associated Press.

The full extent of the damage is not yet known, and the authorities have hesitated to estimate the cost of a cleanup.