The head of the Virgin Group owns small Necker Island in the British Virgin Islands.
He posted several photos on Twitter before Irma hit.
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In a caption on one of the photos, Branson wrote that he and others were going to ride out the storm under the house in his concrete wine cellar.
After the storm rolled through, he said all of his team on the island have been accounted for as safe.
"Necker Island felt the effects of Hurricane Irma and sustained extensive damage, the extent of which we are still assessing. We'd like to thank all of you for your thoughts and would like to assure you that we will be keeping you along, with our family and friends, updated this week as we know more. We will do whatever we can to support and assist our local community through this extremely testing time," Branson said in a blog entry.
In an earlier blog post, Branson said he and his crew "experienced a night of howling wind and rain" and called the atmosphere there "eerie but beautiful."
About sheltering in his concrete wine cellar, he added: "I suspect there will be little wine left in the cellar when we all emerge."
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The Associated Press contributed to this report.