"Don't worry about a thing", President Trump responded.
"I just wanted to pay my respects and we are with you one thousand per cent, you are safe".
North Korean military on Thursday said it would prepare a plan by mid-August to strike Guam, a U.S. island territory in the Western Pacific, with intermediate missiles. "All over the world they are talking about Guam, and they are talking about you".
Mr Trump praised the scenic beauty of the island, which is roughly 3379 kilometres southeast of Pyongyang.
He told the governor, "You seem like a hell of a guy".
"I have to say, Eddie, you're going to become extremely famous".
"As far as I'm concerned, as an American citizen, I want a president that says that if any nation such as North Korea attacks Guam. that they will be met with hell and fury", Calvo said Wednesday on Fox News' "Tucker Carlson Tonight".More news: China willing to pay the price for new North Korea sanctions
More news: Trump tells Guam Governor 'you are safe'
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Former State Department official Joel S. Wit, the founder of 38 North, a website that analyzes North Korea, told Politico that Trump's claims risked undermining diplomatic efforts.
"We are the best in the world by a factor of five", he said.
Calvo, who noted that this is not the first time North Korea has threatened the island, bluntly told Guam residents to simply conduct their daily business "as usual". It included information on how to build an emergency supply kit, make an emergency family plan, make a list of potential concrete shelters near your home, and to not look at the flash or fireball because it can blind you.
Trump, and Chief of Staff General John Kelly, phoned Guam's governor Eddie Baza Calvo to assure him that the people of the country are safe and that the president is behind the them "1000 percent". They called me from the White House this morning and both assured me that the people of Guam are safe.
A video shows Gov. Eddie Baza Calvo laughing and joking with the president as they discuss everything from the readiness of the United States military to tourism.
Guam's $5 billion economy is fueled mainly by tourism and the United States military, which occupies about 30 percent of the island and is looking to expand.