Powerful Hurricane Omar has pummelled St Croix in the US Virgin Islands with heavy rains and winds, sinking boats in the harbour and knocking down trees and power lines across the island.

Omar grew into a Category 3 hurricane with top winds of 115mph and continued strengthening as it headed towards the popular tourists destinations of the US and British Virgin Islands.

The storm sank at least two 30ft boats in Christiansted harbour as it approached on a path projected to bring it just east of the southernmost island in the US Caribbean territory.