London (AFP) - Britain flew additional aid supplies to the Caribbean on Friday after Hurricane Irma flattened homes and schools and flooded hospitals, causing the British Virgin Islands to declare a state of emergency.

The governor of the islands, Gus Jaspert, said in a message to the archipelago, whose 28,000 inhabitants took the full force of the mega-storm, that there had "sadly been reports of casualties and fatalities".

Britain sent a C-17 military transport plane with 50 troops and humanitarian aid on board, heading to Barbados and the British Virgin Islands, while another was to head to the Caribbean later Friday, officials said.

A military ship is also nearby offering assistance, while another laden with more aid has been diverted from the Mediterranean.

Sharon Flax-Brutus, director of tourism for the British Virgin Islands, said that the damage was difficult to assess because communications were down, but that "many homes are without roofs, or have been diminished to merely foundations".

Teresa Brooks, a 23-year-old photographer in London, said her family on nearby Anguilla, another self-governing British territory hit by the storm, reported a "complete disaster".

"The hospital is not functioning properly as it lost its roof during the hurricane and started to flood. The majority of the schools have been complete destroyed," she told AFP in an email.

"Shops have been destroyed as well so there will be no food available. The majority of the poles for electricity have been destroyed so there will be no power for months.

"Tourism -- which is Anguilla's main industry -- will be down for months as most hotels have been destroyed and so there will be no income for many months."

In Turks and Caicos, another British territory struck by the hurricane, the disaster agency said on Twitter: "National shutdown has been declared. All residents & tourists are instructed to stay indoors."

- Response too slow? -

British Prime Minister Theresa May said the impact of the storm had been "absolutely devastating", telling BBC radio: "Everything, for some people, has been destroyed."

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On Thursday her government increased the aid budget for Irma to Â£32 million ($42 million, 35 million euros) from an initial Â£12 million.

The military ship Mounts Bay visited Anguilla on Thursday, where Royal Marines and army engineers helped clear the airport runway and restore power and communication services.

The ship, which was sent to the area before the hurricane hit, was due to deliver tents and water purifying equipment to the British Virgin Islands on Friday.

HMS Ocean, a second ship, has been diverted from the Mediterranean to take further supplies to the Caribbean, including 10,000 buckets for water purification and 5,000 solar lanterns.

But some islanders criticised Britain's relief efforts as too slow.

Dorothea Hodge, a former government official in Anguilla, told The Guardian it was "absolutely disgraceful" it had taken so long for London to respond.

And barrister Josephine Gumbs-Connor, who also lives in Anguilla, told BBC radio she was "very disappointed".

"We have huge trees and some of our oldest trees are still lying across the roads, roads are remaining impassable," she said.

A Downing Street spokeswoman said: "We believe that we were swift to respond and we continue to get humanitarian aid to people in desperate need."

Foreign Office figures show there are currently 88,000 British citizens in the British Overseas Territories of Anguilla, the British Virgin Islands and the Turks and Caicos islands.

Hurricane Irma has been ripping through the Caribbean since Wednesday, with its violent winds and torrential rains leaving a trail of devastation and killing 12 as it hurtles towards the United States, where up to a million people have been told to flee.