Japan has wheeled missile defence systems into the heart of Tokyo after North Korea threatened to send a volley of rockets over the country towards Guam.

Pictures show how a PAC-3 Patriot missile unit has been moved in to a compound at the Defence Ministry in the capital after officials said they could shoot down North Korean rockets if they pass overhead.

Sales of bomb shelters in Japan are said to have increased as tensions continue to rise in the region while officials in Seoul have vowed to bolster their defences. But South Korean citizens - long accustomed to its neighbour's fearsome rhetoric - are staying remarkably calm as the crisis unfolds, it has been reported.

Officials in Hawaii, meanwhile, say they are working on how to warn its 1.4million residents in the event of an attack.

It comes after North Korea warned it will complete a plan to unleash an 'enveloping fire' around Guam by mid-August. This will involved firing four Hwasong-12 missiles over Japan and into waters near the tiny US island, officials claimed.

Japan has wheeled missile defence systems into the heart of Tokyo after North Korea threatened to send a volley of rockets over the country towards Guam

Pictures show how a PAC-3 Patriot missile unit has been moved in to a compound at the Defence Ministry in the capital after officials vowed to shoot down North Korea rockets should they pass overhead

A PAC-3 Patriot missile unit is seen in the compound of Defense Ministry in Tokyo this morning

Officials in Seoul have vowed to bolster their defences. A U.S. Air Force F-16 fighter jet lands on the runway at the Osan base in Pyeongtaek, South Korea, this morning

Tokyo, which has in the past warned it would shoot down any North Korean missiles that threaten its territory, responded that it could 'never tolerate' provocations from the reclusive state.

Defense Minister Itsunori Onodera has said a missile attack on the island would breach the U.S. deterrence against an attack on Japan.

He said that would be a Japanese national emergency because it would threaten Japan's existence as a nation.

Onodera said Japan in that case can exercise the right to 'collective' self-defense and activate the Aegis destroyer ship-to-air missile defense system.

His comment underscores Japan's growing military role and reverses its previous position that it can only shoot down missiles headed to Japan.

A defense law that took effect last year allows Japan's military to defend U.S. and other allies when they come under enemy attack.

Tokyo, which has in the past warned it would shoot down any North Korean missiles that threaten its territory, responded that it could 'never tolerate' provocations from the reclusive state

An A-10 Thunderbolt attack aircraft readies for takeoff at a US air base in Osan, South Korea this morning

A man looks at replicas of a North Korean Scud-B missile (right) and South Korean missiles at the Korean War Memorial in Seoul this morning

A South Korean soldier stands guard at a guard post near the demilitarised zone separating the two Koreas in Paju, South Korea

South Koreans watch a television displaying news broadcasts reporting on North Korea at a station in Seoul

In April it emerged that sales of nuclear shelters and radiation-blocking air purifiers have surged in Japan as North Korea pressed ahead with missile tests in defiance of U.N. sanctions.

A small company that specializes in building nuclear shelters, generally under people's houses, said it had received eight orders in April alone compared with six orders during a typical year.

The company, Oribe Seiki Seisakusho, based in Kobe, western Japan, also has sold out of 50 Swiss-made air purifiers, which are said to keep out radiation and poisonous gas, and is trying to get more, said Nobuko Oribe, the company's director.

Meanwhile, officials in Hawaii have revealed how they plan to respond in the event of a North Korean attack, CNN reports.

Lt. Col. Charles Anthony, director of public affairs for the state's Department of Defense, said: 'If North Korea uses an intercontinental ballistic missile, from launch to impact (in Hawaii) is approximately 20 minutes;

Vern Miyagi, administrator for Hawaii's Emergency Management Agency, added: 'Pacific Command would take about fives minutes to characterize a launch, where the missile is going, which means the population would have about 15 minutes to take shelter.

Show of defiance: Tens of thousands gathered for a huge rally in the centre of Pyongyang yesterday

Pyongyang's volatile dictator (right) warned he was 'carefully examining' plans to make 'an enveloping fire' around the US island of Guam - hours after Donald Trump (left) had told the hermit state it faces 'fire and fury like the world has never seen' over its nuclear programme

Guam, which is known as the 'Tip of the Spear', is home to thousands of American service members and their families at both Andersen Air Force Base and Naval Base Guam

Naval Base Guam (file above) is located on the southwest side of the island. About one-third of the 210-square-mile island is occupied by the military

The crews practiced intercept and formation training, which gave them an opportunity to improve their combined capabilities and tactical skills. Above a B-1B Lancer bomber is pictured during the mission

'It's not much time at all. But it is enough time to give yourself a chance to survive.'

Meanwhile, in South Korea, residents are surprisingly blasé about the current situation, according to the LA Times.

With the country used to the frequent threats issued by Kim Jong-un, many sense that their neighbour is once again 'crying wolf' and will not follow through with its warnings.

University student Han Hyo-jeong, said: 'I have never thought a war would actually happen in my day, even though we are constantly threatened by North Korea.'

Another citizen, Choi Jin-soo, said: 'In case of an emergency, the government will order us where to go and what to do. If we follow directions, we will be safe.'

The government has a warning system which involves alerting civilians via automated messages to their mobile telephones.

More than 3,000 bunkers exist in Seoul with more across the country including in underground train stations and parking garages.

South Korean President Moon Jae-in has called for a 'rebirth' of his country’s defenses in the face of Kim Jong-un's nuclear threats and told commanders he wants to build a 'winning military'. Souh Korean guards are pictured at the country's border with the North today

President Moon Jae-in however, has called for a 'rebirth' of his country’s defenses in the face of Kim Jong-un's nuclear threats and told commanders he wants to build a 'winning military'.

Last night North Korea dismissed as a 'load of nonsense' warnings by U.S. President Donald Trump that it would face 'fire and fury' if it threatened the United States, and outlined on Thursday detailed plans for a missile strike near the Pacific territory of Guam.

North Korea's apparently rapid progress in developing nuclear weapons and missiles capable of reaching the U.S. mainland has fuelled tensions that erupted into a war of words between Washington and Pyongyang this week, unnerving regional powers and global investors.

Trump's unexpected remarks prompted North Korea to say on Thursday it was finalising plans to fire four intermediate-range missiles over Japan to land 30-40 km (18-25 miles) from Guam, adding detail to a plan first announced on Wednesday.

Guam, more than 3,000 km (2,000 miles) to the southeast of North Korea, is home to about 163,000 people and a U.S. Navy base that includes a submarine squadron and a Coast Guard group, and an air base.

The United States and South Korea remain technically still at war with North Korea after the 1950-53 Korean conflict ended with a truce, not a peace treaty.