UPDATED 12.56pm:  Hurricane Irma has left a trail of "absolute devastation" across the tiny Caribbean island of Barbuda after 295 kilometre per hour winds destroyed homes, snapped trees and claimed at least one life.

Gaston Browne, the prime minister of the two-island nation of Antigua and Barbuda, has described the island as "barely habitable" after the powerful Category 5 storm struck early on Wednesday.

"This rebuilding initiative will take years," Browne told local ABS Television Radio after a visit to the island, where he confirmed one person died in the storm.

Describing the scene as "absolute devastation," he said the storm, which also snapped a telecoms tower, had caused estimated damage of some $US150 million ($A187 million).

US authorities are urging residents to prepare for a "record-breaking" hurricane headed toward Florida as the storm known as Irma brings destruction to the Caribbean.

LISTEN ABOVE: Managing Editor of the Orlando Sentinel John Cutter speaks to Larry Williams about the conditions in Florida

"A new and it seems to be record-breaking hurricane heading right toward Florida, Puerto Rico, and other places," US President Donald Trump said on Wednesday.

The category-5 storm with winds of 295 kilometres per hour was one of the most powerful ever recorded in the Atlantic, officials said.

The US territory of Puerto Rico had declared a state of emergency and residents feared the island's electrical system was vulnerable to weeks or months of disruption, broadcaster CNN reported.

Irma had already destroyed several of the strongest buildings on the island of St Martin, local media reported.

The governor of Florida meanwhile warned residents that the approaching hurricane Irma could be more powerful than the strongest storm ever to hit the southern state.

"The storm is bigger, faster and stronger than hurricane Andrew," Governor Rick Scott said, pointing to a storm that devastated the state 25 years ago in August 1992. That storm was the largest to hit the state and the costliest in US history until hurricane Katrina struck in 2005.

Scott warned the entire state to be prepared, stressing the path of the storm was unclear after it is due to hit the Florida Keys, islands off the state's south-west coast, on Sunday.

Irma is just the fifth Atlantic hurricane to have maximum sustained winds of 295 kph or greater, according to Phil Klotzbach, a tropical scientist at Colorado State University quoted by the Weather Channel.

It comes on the heels of Hurricane Harvey, which developed into a category-4 storm in the Gulf of Mexico before slamming into Texas last month and causing widespread damage in Houston and other areas.

NZers in USA

More than 100 New Zealanders are in the firing line of the monstrous Hurricane Irma.

The Ministry of Foreign Affairs and Trade has confirmed 110 Kiwis registered on the SafeTravel website are known to be in the path of the Category 5 storm - the biggest hurricane ever recorded in the Atlantic.

New Zealanders in the path of the hurricane are advised to follow any instructions issued by the local authorities, including any evacuation orders.

They should also keep their family in New Zealand informed of their well-being and contact their airline or travel agent directly if their travel has been disrupted.