The eye of Hurricane Irma, one of the most powerful Atlantic storms in a century, grazed the Turks and Caicos Islands, rattling buildings after it smashed a string of Caribbean islands and killed at least 22 people on its way to Florida.

With winds of about 290 kilometres per hour (km/h), the storm the size of France has ravaged small islands in the Caribbean in recent days, including Barbuda, Saint Martin and the British and US Virgin Islands, ripping down trees and flattening homes and hospitals.

At least 11 people were killed on Saint Martin and Saint Barts, four in the US Virgin Islands, four in the British Virgin Islands, and one each in Barbuda, Anguilla and Barbados.

Late on Friday, Irma made landfall in Cuba as a massive Category 5 storm after it had weakened to a Category 4 hurricane earlier in the day.

Irma's core is expected to hit Florida early on Sunday, but its tropical force storm winds can arrive as early as Saturday morning.

Brock Long, the head of the Federal Emergency Management Agency said on Friday that parts of Florida would be out of electricity for days, if not longer, and that more than 100,000 people may need shelter.

He warned people not to ignore evacuation orders.

"They need to get out and listen and heed the warnings," Long said.

Preparing for Hurricane Jose

Across the Caribbean, shocked locals tried to comprehend the extent of the devastation while simultaneously preparing for another major hurricane, Jose, now a Category 3 and due to hit the northeastern Caribbean on Saturday.

Irma (left, Cat 5) and Jose (right, just upgraded to Cat 3)

Simultaneous major hurricanes for the first time in seven years. pic.twitter.com/qDstJtUDE7 — Eric Holthaus (@EricHolthaus) September 7, 2017

On the left, Hurricane Andrew (1992).

On the right, Hurricane Irma (today).

(images to scale) pic.twitter.com/JCdxuP0tqm — Eric Holthaus (@EricHolthaus) September 7, 2017

"We are expecting inundation from both rainfall as well as storm surge. And we may not be able to come rescue them in a timely manner," said Virginia Clerveaux, director of Disaster Management and Emergencies for Turks and Caicos Islands.

Al Jazeera's Andy Gallacher, reporting from Puerto Rico's capital, San Juan, said: "As things stand, there are three hurricanes in the Atlantic - Irma, Jose and Katia - which hasn't happened since 2010. But it's Irma that poses the biggest threat, with the UN saying 37 million could be affected."

He added: "In the coming hours and days Irma's course will be closely monitored but its track seems set and the impact could be catastrophic."

Barbuda, where one person died, was reduced "to rubble", according to Prime Minister Gaston Browne.

In the British overseas territory of Anguilla another person was killed, while the hospital and airport, power and phone services were damaged, emergency service officials said.

French Prime Minister Edouard Philippe said four bodies were recovered on the tiny French-Dutch island of Saint Martin, which was hit hard.

"It is an enormous disaster. Ninety-five percent of the island is destroyed. I am in shock," Daniel Gibbs, chairman of a local council on Saint Martin, told Radio Caribbean International.

Television footage from the island showed a damaged marina with boats tossed into piles, submerged streets and flooded homes. French President Emmanuel Macron spoke with British Prime Minister Theresa May on Thursday to coordinate an emergency humanitarian response.