Donald Trump has told Guam's Governor North Korea's threat to launch a missile strike near the remote Pacific island will boost tourism, while assuring the politician the US stands behind the territory "1,000 per cent".

Key points: North Korea has announced a plan to launch ballistic missiles into the seas around Guam

North Korea has announced a plan to launch ballistic missiles into the seas around Guam Guam has issued residents with advice on what to do in the event of a nuclear attack

Guam has issued residents with advice on what to do in the event of a nuclear attack Trump has told the US territory's Governor the missile threat has made Guam famous and will boost tourism

"Tourism, I can tell you this — tourism, you're going to go up like 10-fold with the expenditure of no money so I congratulate you," Mr Trump is heard saying on a speakerphone in a video posted to Facebook by Guam's Governor Eddie Baza Calvo.

"We are with you 1,000 per cent, you are safe," he adds.

"You've become extremely famous. All over the world they are talking about Guam, and they are talking about you."

North Korea has announced a detailed plan to launch a salvo of ballistic missiles into the seas around the US Pacific territory of Guam, a major military hub and home to US bombers.

The plan calls for missiles to be fired into the sea about 40 kilometres from the coast of Guam.

'It's paradise … we'll have 110 per cent occupancy'

In the phone call Mr Trump goes on to praise the island's beauty, which he says he has seen in news reports about the missile threat.

"You know, they're showing so much, it's such a big story in the news and it just looks like a beautiful place," he says.

Mr Calvo agrees: "It's paradise. We've got 95 per cent occupancy and after all this stuff comes down we're going to have 110 per cent occupancy."

Before speaking to Mr Calvo, Mr Trump told reporters in New Jersey that he believed Guam would be "very safe" and threatened North Korea with "big, big trouble" if it launched an attack.

The US Pacific territory of Guam is located in the Pacific Ocean. ( ABC News )

Fact sheet tells locals what to do if there's a nuclear attack

However, Guam's security agency has issued a fact sheet with advice on what residents should do in the event of a nuclear attack.

Referring to an "imminent missile threat", it includes advice like: "Do not look at the flash or fireball — it can blind you".

"If an attack warning is issued, take cover as quickly as you can, under concrete structure or below ground if possible," the sheet adds.

"Fallout radiation loses its intensity fairly rapidly. In time you will be able to leave a fallout shelter."

The Government has instructed residents to be proactive and create emergency supply kits, a family emergency plan and a list of concrete shelters in their vicinity.

Visitors to the Homeland Security website are also directed to an American Red Cross guide on how to "shelter-in-place" during a chemical or radiation emergency.

During the phone call Mr Calvo laments criticism of Mr Trump, saying "from a guy that's being targeted, we need a president like you".

Mr Trump agrees, saying "They should have had me in years ago ... frankly you could have said that for the last three presidents."

He then reassures Mr Calvo, who he describes as a "hell of a guy", telling him the US military is "rock solid".

"We are the best in the world by a factor of five," he says.

Missiles would be in the air for 17 minutes, overflying Japan

North Korea says its Hwasong-12 missiles would take just 1,065 seconds to complete their 3,356km flight over Japan before splashing down in waters off the coast of Guam.

If correct, and if the US allows the missiles to launch in the first place, that leaves 17 minutes for tracking stations on land and sea — including the Pine Gap facility near Alice Springs — to calculate, target and try to destroy the missiles.

Tension in the region has risen since North Korea carried out two nuclear bomb tests last year and two intercontinental ballistic missile tests in July.

Mr Trump has said he would not allow Pyongyang to develop a nuclear weapon capable of hitting the United States.

On Wednesday, Mr Trump followed up his "fire and fury" warning with a boast about US nuclear capabilities.

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