Haiti: Hurricane Irma ripped through the Caribbean on Friday, leaving a trail of devastation and killing 17 as it barrelled towards the United States where up to a million people have been told to flee, reports AFP.

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.

"The entire southeastern United States better wake up and pay attention," warned US federal emergency chief Brock Long. "It will be truly devastating."

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 Friday morning, the US National Hurricane Center (NHC) had downgraded Irma to Category Four with maximum wind speeds of up to 155 miles per hour (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 percent of properties demolished.

St Martin, a pristine island resort divided between France and the Netherlands, also suffered the full fury of the storm, as did the French island of St Barthelemy.

France said at least nine people had been killed across its Caribbean territories and seven more were missing.

There were 112 people injured, including two seriously, said Interior Minister Gerard Collomb.