Terrified Cubans who rode out Irma in coastal towns reported “deafening” winds, uprooted trees and power lines, and blown rooftops.

“What’s out there is terrible,” said Gisela Fernandez, a 42-year-old nurse, after the storm whipped the town in Chapara in the province of Las Tunas Friday.

“It’s finished raining, but all night long there were terrible winds.”

Watch: Hurricane Irma pounds Caribbean and is heading for Florida

The governor of Camaguey province, Isabel Gonzalez Cardenas, said her area was “seriously affected”, but there were no immediate reports of casualties. Cuban officials reported “significant damage.”

More than a million people evacuated from vulnerable areas in Cuba.

In Florida, cities on both the east and west coasts of the peninsular state took on the appearance of ghost towns, as nervous residents heeded insistent evacuation orders affecting 5.6 million people.

The storm’s forecast track has shifted slightly, so it now looks bound for Florida’s west Gulf coast instead of the Atlantic coast, with landfall expected Sunday morning in the Florida Keys.

But Irma is so wide that authorities were bracing for destructive storm surges on both coasts and the Keys, the chain of low-lying islands that stretch south of Miami toward Cuba.

And hurricane-force winds are expected to lash the peninsula as it rolls north toward Georgia.

In Key West, police opened a “shelter of last resort” for those foolhardy enough to ignore mandatory evacuation orders.

Flood-prone Miami Beach, also under mandatory evacuation order, has been emptied of people but is bracing for high waters.

“Nobody can be prepared for a storm surge. They can destroy everything,” said David Wallack, a 67-year-old salsa club owner attempting to secure his property on the city’s Ocean Drive.

“We just can pray for the best. You put what you can in a suitcase and hope.”

Across the peninsula the Gulf coast city of Fort Myers also was battening down for Irma’s screaming winds, rain and storm surge.

“This is a worst-case scenario for our city. And our region,” the city’s mayor, Randall Henderson said on CNN.

“We’re taking it very seriously. We are prepared for it.”

Warning that Irma would be worse than Hurricane Andrew – which killed 65 people in 1992 – Florida’s governor said all 20.6 million Floridians should prepare to flee.

Bumper-to-bumper traffic snaked north out of the state, with mattresses, gas cans and kayaks strapped to car roofs.

Cuban-American Orlando Reyes, 82, was forced to flee his assisted living facility in Miami Beach.

“It is frightening,” he said at a shelter in Miami. “We had to leave without a cent, without taking a bath, or bringing anything.”

The storm smashed through a string of Caribbean islands, beginning with tiny Barbuda on Wednesday, followed by the holiday islands of St Barts and St Martin.

Also affected were the US Virgin Islands, Puerto Rico, the Dominican Republic, Haiti and the Turks and Caicos. The Bahamas were spared Irma’s worst.

French state-owned reinsurer CCR estimated Irma had caused 1.2 billion euros (US$1.4 billion) worth of damage to homes, vehicles and businesses in the territories of Saint Martin and Saint Barts.

“Houses are smashed, the airport is out of action,” St Barts resident Olivier Toussaint said.

“Upside-down cars are in the cemeteries. Boats are sunk in the marina, shops are destroyed.”

Meteorologists meanwhile were closely monitoring two other Atlantic storms.

Jose, another powerful Category 4 storm, was heading towards the same string of Caribbean islands Irma has pummelled in recent days.

The deteriorating weather grounded aircraft and prevented boats from bringing relief supplies to hard-hit islands.

Katia, which made landfall in eastern Mexico late Friday as a Category One hurricane, had weakened by Saturday to a tropical depression. Mexico reported two people killed by mudslides unleashed by the heavy rains.

The US military was mobilising thousands of troops and deploying several large ships to aid with evacuations and humanitarian relief, as the Air Force removed scores of planes from the southern United States.

At least two people were killed in Puerto Rico, and many residents were without power.

Another four people were killed on the US Virgin Islands, with a number of badly injured people airlifted to Puerto Rico.

A child died in Barbuda, where 30 per cent of properties were demolished and the entire island has been evacuated.

France said at least 10 people had been killed across its Caribbean territories, with seven more missing. There were 112 people injured, two seriously.

On the Dutch side of Saint Martin island, two people died.

In northwest Haiti, a motorcyclist was missing after trying to cross a flooded river and a number of roads were washed out.