Mark Zuckerberg is said to be building a $100 million Hawaii compound that includes an underground bunker with its own food and energy sources.

The billionaire CEO of Meta has bought swathes of land on the island of Kauai and has begun a construction project shrouded in secrecy.

Workers on the project, including carpenters, security guards and electricians, have been made to sign strict non-disclosure agreements and those who violate the terms are sacked, according to Wired.

Nonetheless details have leaked out, suggesting that Zuckerberg, 39, is building a sprawling complex that could serve as a postapocalyptic refuge in case of civilisational collapse.

The complex, which is partially completed, consists of more than a dozen buildings with at least 30 bedrooms and 30 bathrooms, according to Wired.

It includes two mansions with a total floor area similar to that of a professional American football field.

The compound boasts an industrial-sized kitchen, offices and conference rooms while a nearby wooded area is reminiscent of a James Bond villain’s lair.

There are said to be plans for 11 disk-shaped tree houses connected by rope bridges to allow Zuckerberg and his guests to stay in the treetops while traversing the area.

Perhaps most striking of all, however, are the proposals for a self-sufficient underground bunker. The two central mansions will be joined by a tunnel, according to plans viewed by Wired.

The underground corridor will allow access to a 5,000 sq ft bunker that includes what is described as a living space, a mechanical room and an escape hatch that can be accessed via a ladder.

The door to the shelter will be made of metal and filled with concrete, a method common in bomb shelters.

Amid various global crises, Zuckerberg, who according to Forbes has a net worth of $118 billion, appears to be planning for the worst-case scenario.

His bunker will be self-sufficient, with its own water tank said to be five feet in diameter and 18 feet tall.

And the compound is already producing a variety of food across its 1,400 acres through ranching and agriculture.

Zuckerberg and his wife, Priscilla Chan, spent a reported $170 million buying the land in Hawaii, a process they began in 2014, as well as the $100 million construction costs.

That would make it one of the costliest personal construction projects ever.

The Zuckerbergs say it will be the site of their family home for them and their three children.

A local construction industry official compared the Zuckerberg compound to a military project due to the heightened security and secrecy.

“The only other time you see that is when you’re doing secure military installations,” they told Wired. “For a private project to have an NDA attached to it is very rare.”

The security measures include a 6ft wall blocking views of the project from a nearby road, while guards stand at entrance gates and patrol the surrounding beaches on all-terrain vehicles.

Workers told Wired that colleagues who had violated their NDA, including by posting about the project on social media, had been dismissed immediately.

“It’s fight club. We don’t talk about fight club,” a former employee using the pseudonym of David said. “Anything posted from here, they get wind of it right away.”

The Zuckerbergs have angered the locals with their project, with Hawaiians furious at outsiders buying up vast swathes of the islands and roping it off from the public.

The Facebook founder filed lawsuits in an attempt to force landowners to sell up and was called the “face of neocolonialism” by critics.

Brandi Hoffine Barr, a spokeswoman for the Zuckerbergs, declined to comment on the reports of a bunker, according to Wired.

She said the family are working with conservationists to protect endangered or threatened wildlife in Hawaii.

“Mark and Priscilla value the time their family spends at Koolau Ranch and in the local community and are committed to preserving the ranch’s natural beauty,” she said.

“Under their care, less than 1 per cent of the overall land is developed with the vast majority dedicated to farming, ranching, conservation, open spaces, and wildlife preservation.”

Zuckerberg is not the only tech billionaire apparently planning for end times.

Peter Thiel, an early investor in Facebook, and Sam Altman, the CEO of OpenAI, have an agreement to fly to Thiel’s properties in New Zealand in case of an apocalyptic event, according to the New Yorker.