"Outside of the bunker, bathroom and bedroom doors and windows have flown 40 feet away."
True to form, Branson used his platform to call for donations and support.
"Virgin Unite has made a donation to the British Red Cross to support the hurricane relief efforts, and we are awaiting more information about how else we can best support. I would urge everyone to donate to the British Red Cross through Virgin Money Giving (who are waiving their fees in support of the appeal) to help local communities," he said, with a message to readers in the British Virgin Islands to check in on Facebook to alert family members about their safety.
Branson is the 324th wealthiest person in the world, with a net worth of about US$5 billion ($6.8b), according to Forbes, which notes that he bought Necker Island for US$180,000.
On Thursday, before Irma hit, Branson posted pictures of people smiling and bedded down in a room filled with furniture, backpacks and makeshift beds.
"All of us slept together in two rooms," Branson wrote. "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.
"We were listening to the parrots in their boxes in the next room chattering away. Watching the tortoises congregating together, as if they sense what is coming our way."
A few hours before Irma's impact, Branson wrote that he planned to retreat with his team to his concrete wine cellar below "the Great House". As one does.
"Knowing our wonderful team as I do, I suspect there will be little wine left in the cellar when we all emerge," he wrote on his blog.