Hurricane Irma pummeled the north coast of Cuba yesterday, inflicting"significant damage" as millions of people in the US state of Florida hunkered down for a direct hit from the monster storm.

Irma's blast through the Cuban coastline weakened the storm to a Category Three, but it is still packing 125 mile-an-hour winds (205 kilometer per hour) and was expected to regain power before hitting the Florida Keys early yesterday, US forecasters said.

At least 19 people have been killed since Irma began its devastating march through the Caribbean as a Category Five storm of nearly unmatched power, making landfall late Friday in Cuba on the Camaguey archipelago.

Floridians flee the approaching hurricane. Photo: AFP, Mail online

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

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.

People in shelter homes in Florida. Photo: AFP, Mail online

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.

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 pummeled in recent days.

Katia, which made landfall in eastern Mexico late Friday as a Category One hurricane, had weakened by Saturday to a tropical depression.

The US military was mobilizing 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.