The four “most solid” buildings on Saint Martin, shared by France and the Netherlands, were destroyed, French Interior Minister Gérard Collomb said.
Significant damage is also being reported in the Dutch section.
The category five hurricane, the highest possible level, has sustained wind speeds reaching 295km/h (185mph).
The most powerful Atlantic storm in a decade first hit Antigua and Barbuda, before moving on to Saint Martin and Saint Barthélemy – the French holiday destination popularly known as St Barts.
The storm, tied for the second-strongest ever recorded in the Atlantic Ocean, is charging through the Virgin Islands and headed for Puerto Rico, the southeastern Bahamas and, by the weekend and early next week, Florida and the Southeast U.S.