Residents returning to the Florida Keys archipelago have found Hurricane Irma shredded mobile homes like soda cans and coated businesses with seaweed.
Irma, one of the most powerful Atlantic hurricanes on record before it arrived in the United States, killed 43 people in its rampage through the Caribbean and at least 12 in Florida, Georgia and South Carolina.
On Islamorada Key, one of just three islands where authorities allowed people to return on Tuesday, the aluminium walls of trailer homes had been ripped open by the storm.
At the Caloosa Cove Resort and Marina, concrete pilings meant to hold the dock in place had been knocked sideways and three manatees lolled in the water, drinking from an outflow pump that was spitting water from the side of the dock.
Local authorities told around 90,000 residents of Miami Beach and people from some parts of the Keys they could go home but warned it might not be prudent to remain there. Irma arrived in the Keys on Sunday with sustained winds of up to 215 km/h.
"It's going to take some time to let people back into their homes, particularly in the Florida Keys," said Brock Long, administrator of the Federal Emergency Management Agency. The island chain curves southwest from Key Largo to Key West, linked by bridges and causeways along a nearly 160km route.
More than 6 million homes and businesses were still without power in Florida and nearby states. Florida's largest utility, Florida Power & Light, said western parts of the state might be without electricity until September 22.
The city of Jacksonville, in Florida's northeast, was recovering from heavy flooding.
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Irma destroyed about one-third of the buildings on the Dutch-ruled portion of the eastern Caribbean island of St Martin en route to Florida, the Dutch Red Cross said on Tuesday.
Irma hit the United States soon after Hurricane Harvey, which ploughed into Houston late last month, killing about 60 and causing some $US180 billion ($A224 billion) in damage, largely through flooding.
Insured property losses in Florida from Irma were expected to run from $US20 billion to $US40 billion, catastrophe modeling firm AIR Worldwide estimated.
Treasury Secretary Steven Mnuchin told a New York investor conference that the storm would ultimately boost the economy by sparking rebuilding.
The NHC is monitoring another hurricane, Jose, which was spinning in the Atlantic about 1130km west of Florida. The Atlantic hurricane season runs through November.
