Houses and cars damaged after the passage of Hurricane Irma on the Sint Maarten. Pic/ AFP

Hurricane Irma ripped through the Caribbean yesterday, 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. 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, adding, "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 yesterday 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.

At least two people were killed in Puerto Rico, and more than half of its three million residents were without power. Another four people were killed on the US Virgin Islands. France said at least nine people had been killed across its Caribbean territories. A state of emergency has been declared in the British Virgin Islands where residents spoke of scenes of "total devastation".