Some Japanese bomb shelter companies have reportedly had to implement a waiting list system, while sales of air purifiers have also soared amid fears of a chemical attack.
Even shelter manufacturers overseas have been inundated with enquiries. One US firm based in Texas said it had seen a doubling of requests in recent weeks, of which around 80 per cent were from Japan.
Bomb shelters generally cost the equivalent of several thousand pounds but large ones are on sale for millions.
The Japanese government considered the current threat to be real enough to broadcast a television advert advising people to shelter in a strong building in the event of a missile attack. Some towns and cities have also carried out practice drills.
Experts say a North Korean missile could hit Japan just 10 minutes after being launched.
It comes as South Korean President Moon Jae-in told his military commanders to speed up preparations for protecting the country from a possible missile strike from the north.
Mr Moon is also reported to have asked Donald Trump for permission to produce more powerful ballistic missiles. A current agreement with the US limits the size of missile South Korea is allowed to develop to 500kg. The country wants to raise that to at least 1000kg, The Times reports.
Japan has also said it is considering whether to upgrade its missile capabilities in the face of the mounting threat.
The escalation comes after North Korea announced it was preparing a plan to fire four missiles into the sea off the US territory of Guam.
The threat followed the UN Security Council’s decision to impose new sanctions on North Korea at the urging of the US and its allies.
Donald Trump vowed that North Korea would suffer “fire and fury the like of which the world has never seen” if the threats continued.
US B-1B bombers carried out training drills with South Korean and Japanese jets in a show of force. Further joint military exercises are being planned for later in the month.
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