The worst of the storm is thought to have now passed Necker Island, which sits to the north of the British Virgin Islands' collection of more than 40 islands and islets.
At 10 a.m BST (5 a.m. EDT) Thursday, the billionaire businessman retweeted a message of condolence sent by VirginLimitedEdition to the residents of the Caribbean.
Hours before the storm hit, Branson published a Virgin blog post describing the atmosphere before as "eerie but beautiful."
He and his team spent the previous night together having a "sleepover" reminiscent of his childhood, Branson wrote, sharing a photo on Twitter.
"All of us slept together in two rooms. I haven't had a sleepover quite like it since I was a kid. Strangely, it's a privilege to experience what is turning into possibly the strongest storm ever with such a great group of young people," Branson wrote.
He later said that the team planned to relocate to the wine cellar, adding that little of the wine was likely to remain at the end of their stay.
"Knowing our wonderful team as I do, I suspect there will be little wine left in the cellar when we all emerge," Branson said.
Necker has a large main house and several small Balinese-style houses to accommodate up to 34 people. Branson wrote in a separate blog post Wednesday that the properties were built to withstand severe weather. However, he added that "almost nothing" could withstand a Category 5 storm — the most severe rating.
Hurricane Irma continues to wreak havoc as it rips through the Caribbean, with projections suggesting it could hit Florida on Sunday. So far it has killed at least nine and reduced buildings to rubble.
President Donald Trump said he and his aides were monitoring Irma's progress. "But it looks like it could be something that will be not good. Believe me, not good," he told reporters at the White House.
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