Hurricane Irma has taken a deadly turn with at least six people killed and 900,000 without power on the Caribbean island of St Martin.

The Category 5 hurricane has already destroyed 95 per cent of the island, local official Daniel Gibbs told Radio Caribbean International, calling it "an enormous catastrophe".

"I have a population to evacuate because I don't know where I can shelter them," he said, adding that the island was in dire need of emergency assistance.

French President Emmanuel Macron said it was too soon for casualty figures, but: "I can already tell you the toll will be harsh and cruel."

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As Irma tore through the Caribbean, a tropical storm in the Atlantic and another in the Gulf of Mexico were upgraded to hurricane status today, the US National Hurricane Centre confirmed.

Hurricane Jose was 1675km east of the Lesser Antilles in the Atlantic and packing maximum sustained winds of 120km/h, the NHC said. It was considered a Category 1 hurricane on the five-level Saffir-Simpson scale.

Tropical storm Katia in the south-western Gulf of Mexico had also become a Category 1 storm and a hurricane watch was in effect for the coast of the Mexican state of Veracruz, where heavy rainfall could be expected.

Hurricane Irma, further west, has roared through Caribbean islands with historic 297km/h winds and gusts of 360km/h on its way to a potentially devastating hit on Florida.

The strongest Atlantic Ocean hurricane ever measured destroyed homes and flooded streets across a chain of small islands in the northern Caribbean, passing directly over Barbuda and leaving the island of some 1700 people virtually incommunicado.

Later, Barbuda and Antigua Prime Minister Gaston Browne said the storm had destroyed 90 per cent of the structures on the island. "As it stands, Barbuda is practically uninhabitable," he said.

This is only the second time since satellites started tracking storms about 40 years ago that one has maintained 185kmkm/h winds for more than 24 hours, said Colorado State University meteorology professor Phil Klotzbach. The other was the massive killer typhoon Haiyan that killed more than 6000 people in the Philippines in 2013.

"It's a humdinger," he said. "This thing is a buzz saw; I'm glad Floridians are taking it very seriously," Mr Klotzbach said. "This is going to be a bad storm. I don't see any way out of it."

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The French Minister for Overseas Territories confirmed four fatalities as the hurricane charted a course towards Puerto Rico and Florida.

Two of the dead are from France's Caribbean territories, St Martin and St Barthelemy.
The hurricane has already destroyed 95 per cent of French part of Caribbean island St Martin, officials told AFP.

DEADLY, DEVASTATING IRMA

Irma is threatening millions of people in the Caribbean and Florida.

Sky News weather chief meteorologist Tom Saunders said while Harvey was destructive, Irma is packing a bigger punch.

Dangerous storm surges and record-breaking winds were adding to Irma's destructive impact.

"The winds are much more powerful than with Harvey," Mr Saunders said.

"With mean winds of 295km/h and wind gusts to 360km/h it's certainly up there for the strongest on record."

A man surveys the wreckage on his property after the passing of Hurricane Irma, in St. John's, Antigua and Barbuda. Photo / AP
A man surveys the wreckage on his property after the passing of Hurricane Irma, in St. John's, Antigua and Barbuda. Photo / AP

Irma is the equal strongest storm since Allen in 1980, which caused 269 deaths.

Mr Saunders said hurricanes form over water and dissipate once they hit land.

"The warmer the ocean the more energy is available for a tropical cyclone to form," he said.

Mr Saunders said Irma has more room to grow but Harvey produced more rain because it was moving slower.

"Harvey was a Category 4 so less strong winds (209km/h) but slower in duration and therefore produced more rain," he said.

The most powerful Atlantic Ocean hurricane in recorded history has roared into the Caribbean. Photo / AP
The most powerful Atlantic Ocean hurricane in recorded history has roared into the Caribbean. Photo / AP

However storm surges are expected to be 6m with Irma, which Mr Saunders said would add to the destruction.

Category 5 winds had the potential to uproot trees, signs and tear roofs off homes.
Buildings could also be destroyed while mass evacuations and low escape routes being cut off are also expected under a storm system this strong.

"It's catastrophic damage," he said.

"This storm system is expected to bring storm surges up to 6m to some low-lying areas of the Caribbean," Mr Saunders said.

Mr Saunders said the trio of hurricanes was not uncommon for this time of year, which was peak season.

Irma's strength is partly due to the fact that water in the area is around 1-1.8 degrees warmer than normal.

Irma is just one of three hurricanes in the Atlantic along with Katia and Jose. This last happened seven years ago, according to CNN.

If Irma hits Florida as a Category 4 or 5, it will be the first time in history that the US was hit by two such storms in one year, the Associated Press reported.

Drivers wait in line for gasoline in Florida, ahead of the anticipated arrival of Hurricane Irma
Drivers wait in line for gasoline in Florida, ahead of the anticipated arrival of Hurricane Irma

Forecasters warn Irma could strike the Miami area by early Sunday US time before raking the entire length of the state's east coast and pushing into Georgia and the Carolinas.
Meanwhile multimillion-dollar homes belonging to Johnny Depp, Donald Trump and
Oprah Winfrey are under threat from destructive Irma.

'POTENTIALLY CATASTROPHIC'

The killer storm is so powerful it has registered as seismic activity on some instruments and packs more power than this year's previous eight storms combined, according to a US scientist.

The NHC warned the "potentially catastrophic" hurricane will bring "life-threatening wind, storm surge and rainfall hazards" to the Virgin Islands and Puerto Rico.

Emergency warnings were in effect across the Bahamas, Dominican Republic, Turks and Caicos with Cuba and Florida likely to be hit later in the week.

IT COMES AS:
• The Governor of the British Virgin Islands ordered a 36-hour curfew for residents.
• Emergency evacuations were ordered for six islands in the Bahamas and are expected in the Florida Keys.
• The White House declared a state of emergency in Florida, the US Virgin Islands and Puerto Rico.
• President Trump said it "looks like it could be something that will be not good. Believe me, not good."
• Billionaire Richard Branson was holed up on his private home on Necker Island.
• Hotels issued warnings to guests who described "apocalyptic" noises.
• Storm surges six metres above normal tide levels are expected.
• Puerto Rico residents prepare to be without electricity for four to six months.
• Colorado State University professor Phil Klotzbach warns "the Leeward Islands are going to get destroyed."

'MAY GOD PROTECT US ALL'

The Red Cross said it is bracing for a "major humanitarian response" to the storm made worse by the severe rainfall and isolation of the islands.

Antigua resident Kazia phoned a local radio station to say she was "praying to God" while being hunkered down with no power. Visitors to the island were turned away from the closed airport on Tuesday with the words: "May God protect us all."

CARE Australia's emergency teams said they were working to prepare clean drinking water, food supplies and shelter for residents in Haiti which is still recovering from Hurricane Matthew one year ago.

Video and images posted on social media show the strength of the storm as it moves across the Caribbean and towards the Gulf of Mexico.