More than 17 dead as Hurricane Irma ravages Virgin Islands

So far, 1.2 million people have been affected by Irma, the Red Cross said.

But that number looks set to rise — and could reach as high as 26 million, the agency said. With the monster storm expected to reach the American south by the weekend, coastal areas of Florida and Georgia were battening down the hatches and carrying out their biggest evacuation since 2005. Roaring across the Caribbean, the rare Category Five hurricane laid waste to a series of tiny islands like St Martin, where 60 percent of homes were wrecked, before slamming into the Virgin Islands and Puerto Rico.

By this morning, the US National Hurricane Center (NHC) had downgraded Irma to Category Four with maximum wind speeds of up to 250 kilometres per hour while warning it was still extremely dangerous.

On many islands, violent winds have ripped roofs and facades off buildings, hurling lumps of concrete, cars and even shipping containers aside.

At least two people were killed in Puerto Rico, and more than half of its three million residents were without power after rivers broke their banks in the center and north of the island.

Another four people were killed on the US Virgin Islands, with the governor's office saying a number of badly injured people had been airlifted to Puerto Rico.

One person died in tiny Barbuda which also suffered "absolute devastation," with 300 people evacuated to Antigua and up to 30 per cent of properties demolished.

Meanwhile, Britain's defence ministry said it was sending two military transport planes to the region carrying personnel, supplies and recovery equipment. As European nations quickly mobilized to help their citizens in the Caribbean, French and Dutch ministers said they were sending hundreds of extra police to St Martin tackle a spate of "looting". The storm has caused major shortages of food, water and petrol.

"The situation is serious," Dutch Prime Minister Mark Rutte said today when asked about reports of looting on the island.