A push alert that warned of a ballistic missile heading straight for Hawaii and sent residents into a full-blown panic on Saturday was a mistake, state emergency officials have said.
In a conciliatory news conference, Hawaii officials apologised for the mistake and vowed to ensure it will never happen again.
Hawaii Emergency Management Agency Administrator Vern Miyagi said the error happened when someone hit the wrong button.
"We made a mistake," said Mr Miyagi.
For nearly 40 minutes, it seemed like the world was about to end in Hawaii, an island paradise already jittery over the threat of nuclear-tipped missiles from North Korea.
The emergency alert, which was sent to mobile phones statewide just before 8.10am, said: "BALLISTIC MISSILE THREAT INBOUND TO HAWAII. SEEK IMMEDIATE SHELTER. THIS IS NOT A DRILL."
On the H-3, a major highway north of Honolulu, vehicles sat empty after drivers left them to run to a nearby tunnel after the alert showed up, the Honolulu Star-Advertiser reported.
Workers at a golf club huddled in a kitchen fearing the worst.
Professional golfer Colt Knost, staying at Waikiki Beach during a PGA Tour event, said "everyone was panicking" in the lobby of his hotel.
"Everyone was running around like, 'What do we do?'" he said.
Richard Ing, a Honolulu attorney, was doing a construction project at home when his wife told him about the alert. His wife and children prepared to evacuate while he tried to figure out what was happening.
Cherese Carlson, in Honolulu for a class and away from her children, said she called to make sure they were inside after getting the alert.
"I thought, 'Oh my god, this is it. Something bad's about to happen and I could die,'" she said.
The Hawaii Emergency Management Agency tweeted there was no threat about 10 minutes after the initial alert, but that didn't reach people who aren't on the social media platform.
A revised alert informing of the "false alarm" didn't reach phones until 38 minutes later, according to the time stamp on images people shared on social media.
The incident prompted defense agencies including the Pentagon and the US Pacific Command to issue the same statement, that they had "detected no ballistic missile threat to Hawaii".
The White House said president Donald Trump, at his private club in Florida, was briefed on the false alert.
White House spokeswoman Lindsay Walters said it "was purely a state exercise."
House Speaker Scott Saiki said the system Hawaii residents have been told to rely on failed miserably.
He also took emergency management officials to task for taking 30 minutes to issue a correction, prolonging panic.
"Clearly, government agencies are not prepared and lack the capacity to deal with emergency situations," he said in a statement.
Hawaii Governor David Ige apologised for the "pain and confusion" caused by the alert.
This was my phone when I woke up just now. I'm in Honolulu, #Hawaii and my family is on the North Shore. They were hiding in the garage. My mom and sister were crying. It was a false alarm, but betting a lot of people are shaken. @KPRC2 pic.twitter.com/m6EKxH3QqQ— Sara Donchey (@KPRC2Sara) January 13, 2018
Hawaii US Senator Brian Schatz tweeted the false alarm was "totally inexcusable" and was caused by human error.
"There needs to be tough and quick accountability and a fixed process," he wrote.
Federal Communications Commission Chairman Ajit Pai said on social media the panel would launch an investigation.
With the threat of missiles from North Korea in people's minds, the state reintroduced the Cold War-era warning siren tests last month that drew international attention. But there were problems there, too.
Even though the state says nearly 93% of the state's 386 sirens worked properly, 12 mistakenly played an ambulance siren.
At the tourist mecca of Waikiki, the sirens were barely audible, prompting officials to add more sirens there and to reposition ones already in place.