Hurricane Irma will exact a "heavy, cruel" toll on two French Caribbean islands, President Emmanuel Macron said Wednesday after a crisis meeting with key ministers in Paris.

"It's too soon for casualty figures (but) I can already tell you the toll will be heavy and cruel," a sombre Macron said, flanked by Prime Minister Edouard Philippe and Interior Minister Gerard Collomb. "And the damage on the two islands (St Barts and St Martin) will be considerable."