1.2 million people 'battered' by Irma: Red Cross

"Our worst fears have played out in Barbuda and elsewhere," Walter Cotte, Americas director for the International Federation of Red Cross and Red Crescent Societies (IFRC), said in a statement.

Irma -- one of the most powerful Atlantic storms on record -- has turned the Caribbean islands of Barbuda and St Martin into mountains of rubble.

The Geneva-based IFRC said that Irma "may have already battered an estimated 1.2 million people and poses a serious threat to millions more".

The organisation specified that in the Dominican Republic, Haiti and Cuba "an estimated 26 million people could be exposed to destructive winds and torrential rain."

An initial 600,000 Swiss francs (USD 631,000 / 525,000 euros) in emergency funds have been released to help preparedness efforts in the Dominican Republic and Haiti, the Red Cross said.

"People across the Caribbean will need our help to withstand and then recover from this storm," Cotte said.

"We're already preparing what could become a massive and multi-country response effort."

Irma was packing maximum sustained winds of up to 185 mph (295 kph) as it followed a projected path that would see it hit the northern edges of the Dominican Republic and Haiti today, continuing past eastern Cuba before veering north for Florida.