Two earthquakes, three monstrous hurricanes and the North Korean missile crisis have US survivalists convinced that the end of the world is nigh.

In anticipation of Earth's final chapter they are clearing store shelves to stock bunkers.

Sales of freeze-dried food, gas masks and other survival equipment have spiked in recent weeks as so-called "preppers" get ready to ride out any disaster, whether natural or man-made.

Inspiring their actions: images of people helpless against floodwater from Hurricanes Harvey, Irma and Maria and island towns obliterated by their fury. People buried in rubble after earthquakes rattled Mexico. Footage of North Korea's missiles blazing into the sky.

"It's been a very busy six or seven weeks here - sales tripled practically overnight," said Keith Bansemer, vice president for marketing for Idaho-based My Patriot Supply, an online store catering to preppper needs.

David Yellin, a self-described prepper who lives in California's San Diego County, has piled enough survival supplies for his fiance and their two dogs to hunker down for a month.

If disaster forces the couple to flee, each has a "bug-out bag" stuffed with three days of food, water, first aid and water purification supplies, fire- starting materials, a tent and sleeping bag, change of clothes and important documents.

At Ready To Go Survival, founder and chief executive Roman Zrazhevskiy said gas masks were quickly moving off the shelves and overall sales "are up like 700 per cent over the last two months".

A prepper himself, he said his greatest fear was a US economic collapse as a result of the country's unsustainable debt.