The small US island, which has been caught in the middle of an explosive war of words between President Donald Trump and North Korea, advises its citizens on how to survive an "imminent" missile attack from nuclear-armed Pyongyang.
Trump said he was considering additional sanctions on North Korea, adding that they would be "very strong".
If North Korea launches missiles on Guam, it would take only about 14 minutes for the rockets to reach the USA territory, the island's Homeland Security spokeswoman announced.
It's not the first time North Korea has threatened Guam, which is a crucial, strategic hub for US forces in the Pacific.
The exercises were scheduled well before tensions began to rise over Trump's increasingly fiery rhetoric and North Korea's announcement of the missile plan, which if carried out would be its most provocative launch yet.
"Things will happen to them like they never thought possible, OK?"
Asked if the US was going to war, he said cryptically, "I think you know the answer to that".
According to its reported plan, North Korea would fire four Hwasong-12 intermediate-range missiles over Japan and into waters around Guam, home to about 7,000 troops and 160,000 people.
Jacob Martinez, 29, a purchasing officer at a high-end hotel, said he was frustrated that Guam, an island smaller than Singapore and about 11,000 km away from the US mainland, might be dragged into a major conflict. After the attack, which North Korea has said it would take less than 18 minutes to reach the island, authorities advise Gambians to steer clear of areas marked "radiation hazard" or "HAZMAT" as well as all damaged areas. "I feel it would be a pretty stupid idea to do that", she said.
Clarissa Baumgartner, a 25-year old Guam resident, said Pyongyang's second threat in as many days to train its ballistic missiles on Guam wasn't something she was taking too seriously.
It was not the first time Guam has been put on notice and similar threats made since 2013 led to the USA military permanently deploying a Terminal High Altitude Area Defense (THAAD) interceptor system on the tiny island.
The majority of islanders are ethnically Chamorro - the indigenous group that has lived on the island for thousands of years - and their culture is a touchstone for the islander's way of life.
The governor of Guam, Eddie Baza Calvo, said there had been no change to the threat level on the island, despite the harsh words.
Guam is about 2,100 miles (3,380 kilometers) southeast of Pyongyang and 3,800 miles (6,115 kilometers) west of Honolulu in the Pacific Ocean.
On North Korea's latest warning to hit Guam, South Korean government officials pointed out it was the first time Pyongyang has ever threatened to hit the American island while specifically mentioning the type of missile that would be used, but said the North was probably doing so to save face after the United Nations sanctions were passed.