People in Japan are reportedly rushing to buy bomb shelters amid rising tensions over North Korea’s missile capabilities.

Along with South Korea, Japan is considered to be most at risk from an attack by Pyongyang after continued threats and frequent missile tests that usually land in Japanese waters.

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 told Bloomberg 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. It has also moved missile defence units into the centre of Tokyo in anticipation of a possible rocket attack. Images showed the mobile unit deployed outside the Defence Ministry.

Some towns and cities have also carried out practice drills to make residents aware of what they should do in the case of an attack.

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.

In pictures: North Korea military drill Show all 8 1 /8 In pictures: North Korea military drill In pictures: North Korea military drill North Korea's leader Kim Jong Un watches a military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) is seen in this handout photo by North Korea's Korean Central News Agency (KCNA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) is seen in this handout photo by North Korea's Korean Central News Agency (KCNA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video

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.