Guam residents should take cover from a North Korean missile attack quickly, in a concrete structure, preferably underground - and stay there until told otherwise, a survival guide advises.
The US island territory's Office of Civil Defence began distributing fact sheets, Preparing for an Imminent Missile Threat, on Friday, to help people prepare for an attack.
The guidance includes tips on building an emergency kit, advice on staying put in concrete or brick structures, and reminders about keeping calm.
"Do not look at the flash or fireball - it can blind you", the fact sheet advises those who are caught outside.
"Lie flat on the ground and cover your head."
The leaflet also offers guidance on removing radioactive material, saying: "When possible, take a shower with lots of soap and water to help remove radioactive contamination."
But do not scratch or scrub skin and "do not use conditioner because it will bind radioactive material to your hair".
Officials have not raised the territory's threat level even after Pyongyang laid out plans to strike near the island in the coming weeks, Guam governor Eddie Calvo said.
He noted that Guam had many buildings made to withstand powerful typhoons, but acknowledged that nothing could protect against a thermonuclear attack.
US president Donald Trump assured Mr Calvo that Guam was safe, during a phone call.
"We are with you a thousand percent," Mr Trump said, according to video of the call posted on Mr Calvo's Facebook page. "You are safe."
Mr Calvo responded by saying he feels safe and confident with Mr Trump's leadership.
"I'm glad you're holding the helm, Sir," he said.
The fact sheets did not seem to cause any widespread anxiety or affect day-to-day Guam life.
Some people wondered about finding plastic sheeting, as one of the leaflets recommends using that and duct tape "to seal all cracks around the door and any vents into the room".