Milton Torres is worried about the state of the world — so worried that the 42-year-old biomedical engineer has packed up his life and moved to a remote, underground bunker in the Midwest of the United States.

Milton Torres, outside his bunker in South Dakota, says he "doesn't even know what's real anymore". ( Supplied: The Vivos Group )

He's part of a growing number of Americans preparing for social, economic and environmental collapse.

"I don't even know what is real or not anymore," Mr Torres says.

"They have us so confused, but they don't want to panic the people about what's happening.

"You think the government is going to save you? If you think that, good luck."

Mr Torres is the first to move permanently into Vivos xPoint, a community of 575 bunkers designed to accommodate up to 5,000 people in a former army munitions site in South Dakota.

He paid $US25,000 for a 200-square-metre underground bunker, which can survive water, air, and gas penetration, as well as significant internal and external explosions.

"It's a steal — especially when compared to a house that won't survive a meteor strike," he says.

A growing number of Americans preparing for social, economic and environmental collapse by moving into bunkers. ( Supplied: The Vivos Group )

Bunker economy enters mainstream society

Mr Torres is part of what anthropologist Chad Huddleston of South Illinois University sees as an emerging middle-class prepping movement made up of highly educated people with good jobs earning a decent salary.

Tom Soulsby outside his bunker in South Dakota. ( Supplied: The Vivos Group )

Dr Huddleston has tracked the "prepping" movement for years, and says the bunker economy shows it has entered mainstream society.

"Preppers want to keep up their standard of living, even though the outside world might be burning," he says.

"Those who can afford it think that at least they and their family will emerge unscathed from their bunker after an event.

"The prepping mentality is something we should all be doing a little."

This rings true for Tom Soulsby, one of Mr Torres's new neighbours in South Dakota.

The IT worker was planning a more traditional retirement until he saw an ad for the bunkers on Facebook three years ago.

"When you consider that everyone keeps food in their pantry, they're preparing. We carry that a bit further," he says.

Mr Soulsby, based in Georgia, has a bunker that serves as an escape shelter, a holiday home, and a retirement plan in one.

"It's far enough away so if it's a regional event, it won't affect me," he says.

"It's resilient enough so that if civil unrest occurs, I can button up there and be safe."

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Dr Huddleston says what led to growing demand for bunkers was in fact a very real disaster unfolding on television: Hurricane Katrina.

"After Katrina, people started to think that the government is not going to come and save them," he says.

"There seems to be a shift in how people are thinking about disasters, they can see that they're becoming more common due to climate change."

Mr Soulsby echoes this mentality.

"We've seen in the last few years how fragile our infrastructure is and how little disruption it takes to disturb our lives," he says.

"Look at Hurricane Harvey two years ago — some of those people still aren't home."

'It's life insurance for their heirs'

This pool is one of the shared features offered by Survival Condo. ( Supplied: Survival Condo Project )

Owner of The Vivos Group, Robert Vicino, has built three bunker communities in the United States in the past 10 years, as well as luxury facilities in undisclosed locations catering to the ultra-wealthy, where some individual bunkers are "the size of a Walmart".

Vivos will soon open communities in Germany and South Korea, and Mr Vicino says they receive "lots of enquiries" from Australians.

"Our locations can hold up to 10,000 like-minded people all carrying guns in an area three-quarters the size of Manhattan," he says.

"They become their own army, because that's the nature of survival.

"It would be suicide to invade that facility, unless you're Russia, China or America."

The Survival Condo complex boasts a rock-climbing wall for fitness. ( Supplied: Survival Condo Project )

While Mr Vicino had a vision of an apocalyptic future some 30 years ago, it wasn't until the global financial crisis hit that he put aside his other business interests and started building bunkers.

"Everyone is going to see that there is a need for these — unfortunately for most it will be too late," he says.

"We are effectively nothing more than insurance: you hope you don't have to use it, but if you do, it's priceless.

"For the elite, it's life insurance for their heirs. Not doing so would be reckless."

While many clients are focused on the protective features of their bunkers, it's also what's on the inside that counts.

"Our luxury nuclear hardened bunker full-floor unit is the most requested offering," says Larry Hall, owner of Survival Condos.

"This is a 1,840-square-feet condominium that has three bedrooms, two bathrooms, and luxury finishes that sells for $US3 million."

Shared features include an organic hydroponic and aquaculture food production system, a bar and lounge, pool and spa, digital weather station, and an indoor shooting range.

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'An end to this extraction and pollution is coming'

Gary Lynch from Texas-based Rising S Bunkers agrees there is a socio-economic profile to his clients, but believes the common thread is political.

"We get a lot of enquiries from Silicon Valley, but the most notable thing is that 99.5 per cent of our clients are conservatives," he says.

"They are more responsible and more aware of what the possibilities are. It's liberty or death — and it's up to you to come and take it."

Mr Lynch says that in 2016 there was a 700 per cent increase in bunker sales at his company, with many clients citing fear of war with North Korea.

Their bunkers retail from anywhere between $US39,500 to $US14 million, and have been installed in secret locations around the world.

Survival Condo's general store, offering "shelf reliance" and "fresh bread". ( Supplied: Survival Condo Project )

It's difficult to say whether the craze started or simply caught on in Silicon Valley, which is home to half of the world's billionaires.

But in 2017, LinkedIn co-founder Reid Hoffman estimated that about half of the region's tech billionaires had become preppers.

This concerns Douglas Rushkoff, academic and author of Team Human.

"The billionaires figure they need to earn enough money simply to insulate themselves from the problems they're creating," he says.

"It's the same sort of mindset that leads Trump to want to build a wall to protect Americans from the Mexican 'invasion'.

"There's a tendency in the tech community to think of human beings as the problem, and technology as the solution.

"These attitudes engender an anti-human sensibility among the wealthy. They see the masses as a resource from which to extract value — not a population of peers with whom to interact.

"And they know this can't go on forever. Whether it's climate change or social unrest, an end to this extraction and pollution is coming."

Community members Michael and Megan Gembala (left) talk with Vivos owner Robert Vicino inside their bunker. ( Supplied: The Vivos Group )

For Mr Rushkoff, the solution isn't to bunker down.

"We just can't let billionaires extract all of the planet's wealth and resources as they do," he says.

"We need to push back on an economic system that values corporate growth over human survival."

Elle Hardy is a freelance writer based in the United States.