“We took shelter from the strongest hurricane ever inside the concrete cellar on Necker and very, very fortunately it held firm,” Branson, founder of the Virgin business empire, said in a blog post.
“I have never seen anything like this hurricane. Necker and the whole area have been completely and utterly devastated,” he said, adding that he and his staff were all “safe and well”.
“We are still assessing the damage, but whole houses and trees have disappeared.
“Outside of the bunker, bathroom and bedroom doors and windows have flown 40 feet (12 metres) away.”
“I’m speaking these words from a satellite phone that is just about working, but all other communications are down,” he said.
Branson said his company had made a donation to the British Red Cross and a Virgin Atlantic flight to Antigua on Thursday had brought in aid supplies including blankets and bottled water.
But he said the British Virgin Islands, where his island is located, would need “major help to rebuild people’s homes, buildings, livelihoods” and urged the British government to “send as much help as possible”.
Branson started out his business in London in 1970 to sell discount music records.
Proceeds from the shop helped build a recording studio, and Virgin Records came into being in 1972.
The company has since diversified into air travel, railways, healthcare and banking.
Branson’s mane of blond hair and goatee beard made him one of the world’s most recognisable businessmen.