MIAMI — Millions of Florida residents were without power and extensive damage was reported in the Florida Keys but most of the Sunshine State appeared on Monday to have dodged forecasts of catastrophic damage from Hurricane Irma.

While Florida may have escaped the worst from the monster storm which first pummeled the Caribbean, the death toll jumped to at least 40 as Cuba said 10 people had been killed there over the weekend as Irma spun northward.

And in the Caribbean, as hard-hit residents struggled to get back on their feet, Britain, France, the Netherlands and the United States ramped up relief efforts for their overseas territories.

Florida residents who spent an anxious night huddled indoors were venturing out to survey the damage, which did not seem to be as bad as initially feared.

More than 6.5 million customers in Florida were without power, however, and Governor Rick Scott said the chain of southern islands known as the Florida Keys had suffered a lot of damage.

"There’s devastation," Scott said after flying over the Keys with the Coast Guard. "I just hope everybody survived. It’s horrible what we saw."

He said the water, electricity and sewage systems in the Keys were all non-operational and that trailer parks had been "overturned."

Most Keys residents had followed mandatory evacuation orders, but there were some holdouts who had to hunker down as Irma slammed into the low-lying tourist archipelago known for its fishing, scuba diving and boating.

Footage from the Grassy Key island shot by US broadcaster NBC showed downed power lines, felled trees and streets strewn with debris and vehicles. But homes that were made from concrete appeared to have withstood the gusts.

Irma now a tropical storm

Irma was downgraded to a tropical storm, but forecasters warned of "life-threatening" storm surges, heavy winds and risk of tornadoes.

Florida’s northeastern city of Jacksonville, population 880,000, ordered urgent evacuations amid record flooding along the St Johns River.

Flooding was also reported in the city of Charleston, South Carolina, and the National Hurricane Center warned of possible isolated tornadoes in the state.

Irma’s maximum sustained winds had decreased to 72km per hour as of 8.00pm (local time). Irma’s eye was in western Georgia, and expected to cross into eastern Alabama on Tuesday.

Irma had triggered orders for more than six million people in the US to flee to safety, one of the biggest evacuations in the country’s history.

The storm roared ashore on the Keys on Sunday as a powerful Category Four hurricane, ripping boats from their moorings, flattening palm trees and downing power lines, after devastating a string of Caribbean islands.

In flood-prone Miami, the largest US city in Irma’s path, cleaning crews were busy clearing branches, debris and fallen street signs from downtown.

Mayor Carlos Gimenez expressed relief that the damage wasn’t worse.

"We were spared the brunt of this storm," Gimenez said. "We came out much better than other parts of the state and we have to thank God for that."

10 dead in Cuba

In Bonita Springs, a city of 50,000 people on Florida’s hard-hit southwest coast, large areas were flooded and the entire city was without power. Some residents were trying to reach their homes by walking through floodwater up to their waists, while others paddled canoes.

"I don’t think I can make it over to the house. I’d like to walk through there, but it looks like it’s one metre deep at least, and my boots are only a foot deep and I don’t like cold water, which explains why I live here," Sam Parish said.

As residents began to check out their homes, authorities warned of downed power lines, raw sewage in floodwaters and – this being Florida – displaced wildlife like snakes and alligators.

"Don’t think just because this has passed you can run home," Governor Scott said. "We have downed power lines all across the state.

"We have roads that are impassable," he said. "We have debris all over the state."

President Donald Trump has approved the state’s request for emergency federal aid to help with temporary housing, home repairs, emergency work and hazard mitigation. He has promised to travel to the state "very soon."

Before reaching the United States, Irma smashed through a string of Caribbean islands from tiny Barbuda on Wednesday, to the tropical paradises of Saint Barthelemy and Saint Martin, the US Virgin Islands, Puerto Rico, the Dominican Republic, Haiti and the Turks and Caicos.

About 400 exhausted and traumatized survivors of Hurricane Irma arrived in France and the Netherlands on Monday aboard military planes.

A plane with 278 aboard landed in Paris, while another 100 people flew into Eindhoven in the southern Netherlands from the Guadeloupe capital Pointe-a-Pitre.

Both the French and Dutch governments have come under criticism over delays in their responses to the crisis and in particular over how they handled outbreaks of looting on Saint Barthelemy and Saint Martin, an island with both French and Dutch sectors.

In Cuba, officials said Irma was the deadliest hurricane to strike the island since Dennis in 2005, and warned the toll could rise.

Three quarters of the population were without power as the authorities began the task of restoring basic infrastructure and services.

President Raul Castro warned Cubans they faced "hard days" ahead to rebuild "what the winds of Hurricane Irma have tried to wipe out."  — AFP