US President Donald Trump has threatened to unleash "fire and fury like the world has never seen”, while North Korea retaliated by saying it was preparing for a strike on the US-territory of Guam.
Earlier this week, owner of Atlas Survival Shelters Ron Hubbard, said: “It’s crazy, I’ve never seen anything like it.
“It’s all over the country. I sold shelters today in North Carolina, Tennessee, Texas, Oklahoma, Louisiana, Oregon, Washington, Arizona, California.”
He claimed that he had sold more than 30 units in recent days, including to customers in Japan.
His company, based in eastern Los Angeles, sells shelters priced from £7,734 ($10,000) to £77,340 ($100,000).
The shelters are designed to be buried 20 feet below ground and can sustain survivors for up to one year, depending on the size and model, according to Mr Hubbard.