Nearly two-thirds of homes in Florida are without power
Four storm-related deaths have been reported so far in Florida
The weakening storm is crossing into Georgia
At least 37 people were killed as Irma rolled across the Caribbean
Alison Strand, originally from Staffordshire in the UK, spoke to the BBC while preparing for her home to be hit by the hurricane in Anguilla.
She said she had lost power and was facing "quite dangerous" conditions.
Hurricane Irma: Briton Alison Strand prepares
There are currently hurricane watches and warnings in place for:
The islands' populations range from about 2,000 each on Barbuda, Saba and Culebra, to 3.5 million in Puerto Rico.
Haiti, the Turks and Caicos Islands and the south-eastern Bahamas are on hurricane watch.
And here's a predicted path of Hurricane Irma
Our reporters Laura Bicker, external and Paul Blake, external are in Puerto Rico to cover the fast developing story.
On Tuesday, President Donald Trump declared a state of emergency on the island, which is a territory of the US.
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Irma first hit Antigua and Barbuda, before moving on to St Barthelemy and St Martin.
The storm is then expected to move on towards Puerto Rico and the Dominican Republic.
Meanwhile, in the US, Florida's Key West area has ordered a mandatory evacuation.
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Infrared image of Irma, 4 September
Here's our visual guide, which includes satellite and infrared images of the storm, and shows its path and strength.
The four "most solid" buildings on the island of St Martin, an overseas French territory, have been destroyed, French Interior Minister Gérard Collomb announced.
Here's some footage from St Martin.
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Welcome to our live coverage as Hurricane Irma, the most powerful Atlantic storm in a decade, is battering the Caribbean.
The category five hurricane, the highest possible level, has sustained wind speeds reaching 300km/h (185mph).
It has already caused major flooding and damage to buildings on several islands including St. Martin, with officials warning of its "potentially catastrophic" effects.
We'll be bringing you all the latest updates from our correspondents in the region and witnesses, and also be posting videos and pictures as the storms sweeps through the region.