Four people have been killed by Hurricane Irma in the British Virgin Islands, officials have said.

Hurricane Irma roared through the 40 small islands of the British Virgin Islands late on Wednesday, causing major damage to the largest and most populated island of Tortola.

The Caribbean Disaster Emergency Management Agency confirmed the deaths in a statement on Friday but gave no further details.

The British government has been coordinating relief efforts to the cluster of islands near Puerto Rico and the US Virgin Islands. The Caribbean disaster agency says the Tortola airport is operational but the tower has been "compromised".

At least 20 people are believed to have been killed in the region as the storm ravaged the Caribbean, with a further three people dead on the British island of Antigua, Barbuda and the Dutch side of St Martin, four dead in the US Virgin Islands and nine on the French side of St Martin and St Barts.

Officials say they expect the death toll on the island to rise once they are able to begin recovery operations.

It comes as the UK announced it was sending hundreds of troops and the Royal Navy flagship HMS Ocean to Anguilla, Montserrat and the British Virgin Islands to help with the relief effort.

In a statement, Foreign Secretary Boris Johnson said: "The UK government is responding to the catastrophic damage that has been caused by Hurricane Irma to the Caribbean and in particular obviously to the overseas territories, Anguilla, and the British Virgin Islands.

"Our thoughts go out to the people who have been affected, to those families who have lost loved ones, and as you can expect we are doing everything we can with humanitarian relief and assistance.

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"We have the fleet auxiliary boat RFS Mounts Bay is in the vicinity, we have people on the ground.

"But what we will be doing now is making an urgent assessment of the further needs of communities in the British Virgin Islands and Anguilla to see what more can be done in terms of financial and humanitarian assistance."

In Anguilla, officials reported extensive damage to the airport, hospitals, shelters and schools and said 90 percent of roads were impassable.

On Barbuda, nearly every building was damaged when the hurricane's core crossed almost directly over the island early Wednesday. About 60 percent of its roughly 1,400 residents were left homeless, Antigua and Barbuda Prime Minister Gaston Browne said.

He said roads and telecommunications systems were wrecked and recovery would take months, if not years.

"It is just really a horrendous situation," he added.

The storm has continued to batter the Caribbean archipelago. The hurricane rolled past the Dominican Republic and Haiti before smashing into the Turks and Caicos Islands – another British Overseas Territory – early on Friday morning with waves as high as 20 feet.

Communications have gone down as the storm slammed into the islands and the extent of the devastation is currently unclear.