The erroneous message was sent after months of tensions between Washington and Pyongyang over North Korea's nuclear ambitions.
An alert warning of an incoming ballistic missile aimed at Hawaii was sent in error on Saturday, sowing panic and confusion across the US state - which is already on edge over the risk of attack - before officials dubbed it a 'false alarm'.
Emergency management officials eventually determined the notification was sent just after 8:00am (1800 GMT) during a shift change and a drill after "the wrong button was pushed" - a mistake that lit up phones across the archipelago with a disturbing alert urging people to "seek immediate shelter."
The erroneous message came after months of soaring tensions between Washington and Pyongyang, with North Korea saying it has successfully tested ballistic missiles that could deliver atomic warheads to the United States, including the chain of volcanic islands.
"I deeply apologize for the trouble and heartbreak that we caused today," said Vern Miyagi, administrator of Hawaii's Emergency Management Agency.
"We've spent the last few months trying to get ahead of this whole threat, so that we could provide as much notification and preparation to the public.
"We made a mistake," he told journalists. "We're going to take processes and study this so that this doesn't happen again.
"The governor has directed that we hold off any more tests until we get this squared away."
As social media ignited with screenshots of the cell phone emergency warning, Representative Tulsi Gabbard quickly tweeted that it was a "FALSE ALARM," with Hawaii's EMA confirming "there is NO missile threat to Hawaii."
US military spokesman David Benham later said US Pacific Command "has detected no ballistic missile threat to Hawaii. Earlier message was sent in error."
The warning - which came across the Emergency Alert System that authorities nationwide use to delivery vital emergency information - read: "BALLISTIC MISSILE THREAT INBOUND TO HAWAII. SEEK IMMEDIATE SHELTER. THIS IS NOT A DRILL."
A corrected message indicating that "there is no missile threat or danger to the state of Hawaii" was not dispatched to phones until nearly 40 minutes later.
"There was no automated way to send a false alarm cancellation," said Governor David Ige. "We had to initiate a manual process. And that was why it took a while to notify everyone."
"I know firsthand that what happened today was totally unacceptable," Ige said of the alert, which was also broadcast on some local television stations.
"I'm sorry for that pain and confusion that anyone might have experienced."
SBS News reporter Greg Dyett, was on the Hawaiian island of Maui at the time of the warning, said there was mass panic.
"I also grabbed my mobile and noticed I'd received the same alert and we eventually found a TV station that had an audio alert running of what turned out to be a false alarm," he said.
"After a minute or so on Twitter, I was relieved to see a post from my colleague Brett Mason who had re-tweeted a local politician who confirmed that the alert was a false alarm."
Senator Brian Schatz of Hawaii called the mistaken notification "totally inexcusable," blaming it on "human error."
"There needs to be tough and quick accountability and a fixed process," he tweeted.
The Federal Communications Commission said it was launching a "full investigation" into the incident.
Though the alert was quickly deemed false, many Hawaii residents heeded the nerve-wracking warning, taking refuge in hallways and basements.
Lauren McGowan, on holiday in Maui with family members and friends, was on her way to breakfast when her phone blared the alert.
She and her family quickly returned to their hotel, where staff ushered them along with some 30 people to a basement cafeteria and distributed water and food.
The alert and rush to shelter caused "confusion," McGowan said, particularly for the children in the group.
"No one had any idea what was really going on," the 28-year-old from New York told AFP, explaining they had no cell service underground.
"It was a bit jarring for sure," she said of the experience.
But McGowan added, "I'm not going to let it ruin the rest of my vacation" and it's "definitely good to know that the system works."
Several golfers participating in the US PGA Tour's Sony Open in Honolulu also reacted to the alarming episode.
"Under mattresses in the bathtub with my wife, baby and in laws," American golfer John Peterson tweeted. "Please lord let this bomb threat not be real."
No time for 'posturing'
Tourists and residents received the false alert just one month after Hawaii tested its nuclear attack siren system. The state will conduct the drill - the first of its kind since the Cold War era - monthly as part of its regular siren test, an emergency management official told AFP.
US President Donald Trump - who in the past has deployed bombastic rhetoric at North Korea and its leader Kim Jong-Un - had yet to react to the warning.
The US leader recently said he would be willing to speak directly with Kim, with whom he has traded sharp words over Pyongyang's missile and nuclear tests, raising fears of attacks.
Democratic Representative Tulsi Gabbard, who tweeted minutes after the alert went out that it was erroneous, accused Trump of not taking nuclear threats from North Korea seriously.
"Donald Trump is taking too long. Now is not the time for posturing," Gabbard said.
"He must take this threat seriously and begin direct talks with North Korea, without preconditions, to de-escalate and denuclearize the Korean peninsula.
"The people of Hawaii experienced that in 15 minutes they and their families are going to be dead," she wrote. "Gone. That's what they just went through."