Hawaii's emergency management leader has resigned after it was revealed the employee who sent a ballistic missile alert earlier this month really believed the state was under attack.

Key points: The alert warning was mistakenly sent by a man in his 50s

The alert warning was mistakenly sent by a man in his 50s He says he now fears for his safety

He says he now fears for his safety The alerts agency had no plan on how to correct a false warning

The false alarm went uncorrected for 38 minutes and caused widespread panic across the state. The man who sent it was fired on Friday.

Hawaii's Governor David Ige had said an employee at the state emergency management agency pushed the "wrong button". But the US Federal Communications Commission (FCC) gave a different explanation.

The FCC has blamed miscommunication and a lack of supervision during a test drill

It said in a report the Hawaii Emergency Management Agency worker responsible for the alert believed an attack was real because of a mistake in how the drill was initiated during a shift change.

The worker said he didn't hear the word "exercise" repeated six times during the drill even though others clearly heard it. The recording otherwise used language that is typically used for a real threat, including the words: "This is not a drill."

The FCC said there was no requirement to double-check with a colleague or get a supervisor's approval before sending the alert to mobile phones and TV and radio stations across the state.

"There were no procedures in place to prevent a single person from mistakenly sending a missile alert," FCC lawyer James Wiley said.

As well, software at Hawaii's emergency agency used the same prompts for both test and actual alerts.

It also used prepared text that made it easy for a worker to click through the alerting process without focusing enough on the text of the warning that would be sent.

The worker involved had a history of poor performance

The state of Hawaii said in a report the worker, whose name was not revealed, had confused real-life events and drills in the past.

His poor performance had been documented for years, and other members of the team said they were not comfortable working with him in any role.

Once the employee sent the false alert, he was directed to send a cancel message but instead, "just sat there and didn't respond", the state report said.

Later, another employee took over the computer and sent the correction because the worker, "seemed confused".

The emergency agency has taken steps to avoid a repeat

The FCC said the Hawaii Emergency Management Agency's measures include more supervision of drills and alerts.

As well, it's created a correction template for false alerts and has stopped ballistic missile defence drills until its own investigation is done.

There will also be new leadership after the agency's top two civilian officials resigned.

ABC/wires