Hurricane Maria strengthened to a Category Two storm Monday with maximum sustained winds of 110 miles (175 kilometers) per hour as it menaced Caribbean islands already hard-hit by megastorm Irma.

The US National Hurricane Center expected Maria to grow into a "major hurricane" -- a Category Three -- later Monday with the French territory of Guadeloupe -- the staging area for relief operations for several islands battered by Irma -- in the crosshairs.

Warnings were also triggered for Dominica, St Kitts and Nevis and the British island of Montserrat.