His trip follows criticism from Caribbean residents and senior MPs that the UK's response was too slow.
French President Emmanuel Macron arrived in Guadeloupe today in the first step of his visit to French Caribbean islands hammered by Hurricane Irma.
Water, food and other supplies were being ferried in to the two hardest hit islands, St. John and St. Thomas, where sustained winds of 150 miles an hour flattened homes, toppled beachfront palm trees and left many mountain forests virtually denuded of greenery when Hurricane Irma passed through last week.
We will support the mid to long term efforts on the ground and help provide support as those affected recover from the disaster.
"We just heard from them about 30 minutes before this interview", Kasey Louis said, explaining there was no word from her sister since Tuesday.
At least 34 people were reported to have been killed in the region, including 10 in Cuba, whose northern coast was raked by the storm. The government did not release details about the victims.
Dutch Prime Minister Mark Rutte said the situation remained "grim" on the island where widespread looting had broken out and a state of emergency was in force.
There are just under 500 troops now in the region, made up of marines, engineers, medics and specialists, including Army and Royal Air Force personnel, the Foreign Office said. About one million customers lost power in Puerto Rico after the storm raked the northeastern side of the island territory of 3.4 million residents. French authorities said some 1,105 recovery workers were deployed on St. Martin and St. Barts. Many people were trapped in their homes, and some on lower levels who hadn't evacuated had to be rescued as the water continued to rise.
But he said money offered by the government so far was "not enough".
Amid claims from British tourists on the island that they had been left without food and forced to forage for coconuts in one beach resort, holiday company Thomson said it was planning a mass evacuation of its 2,350 customers in the coming days. "It is truly heart-breaking to see such devastation in a place we call home and to communities we love dearly". The island is shared between a French territory and the former Dutch colony of St. Maarten, a largely autonomous part of the Dutch kingdom with a population of around 40,000.
Low-lying areas of Central Havana often flood during heavy rains or winter storms, but neighbors said they had never seen anything like the high water that Irma pushed ashore. "So I'm a little out of my comfort zone here".
An aerial view of the Virgin Islands - both British and US - shows in stark terms just what is left now: roofs torn off houses, trees uprooted, whole neighborhoods turned into rubble under the weight of the storm. He was expected to reach Barbados on Tuesday.
Anguilla, Turks and Caicos, and the British Virgin Islands (BVI) are among 14 British overseas territories which are all self-governing but the British government is responsible for their defence and security, with a duty to protect them from natural disasters.
Duncan said a total of nine people died in British Caribbean territories - five in the BVI and four in Anguilla.