"Hawaii — this is a false alarm," US lawmaker Tulsi Gabbard, who represents the state, announced on Twitter. "I have confirmed with officials there is no incoming missile to Hawaii."
The alert sent to cellphones said in all capital letters: "Ballistic missile threat inbound to Hawaii. Seek immediate shelter. This is not a drill."
Gabbard said every mobile phone on Hawaii got the text message. People were thinking, "we've got 15 minutes before me and my family could be dead," she told broadcaster CNN. They were told to take shelter, but there are no nuclear shelters to run to, she added.
The Hawaii Emergency Management Agency's administrator, Vern Miyagi, said he took responsibility for the mistake. He said officials would study the error to make sure it did not happen again.
'Pain and confusion'
Hawaii Governor David Ige apologized to the state's residents for the "pain and confusion" caused by the false alarm.
"This should not have happened. We are investigating the sequence of events that occurred," Ige said. "An error was made in Emergency Management which allowed this false alarm to be sent."
In a news conference on Saturday, Ige vowed to launch an evaluation of the alert system and ensure that such a mistake never happened again. He also dismissed claims the alert may have been the result of a hack attack.
About 10 minutes after the initial alert, the Hawaii Emergency Management Agency posted on Twitter and Facebook saying there was no threat, but these messages didn't reach people who weren't on the social media platform.
A mobile alert informing of the false alarm didn't reach cellphones until about 40 minutes later, due to authorization being needed from the Federal Emergency Management Agency's Integral Public Alert and Warning System.
State officials told reporters that the message was mistakenly sent out during a shift change when an employee "pushed the wrong button" at Hawaii's Emergency Management Agency.