The Federal Communications Commission (FCC), in a preliminary report released on Tuesday, said the unidentified officer with the Hawaii Emergency Management Agency (HEMA) claimed not to have heard a phrase warning that it was just an exercise.

At the same time, the report said, the sentence "This is not a drill" was mistakenly included in the recorded message which prompted the officer to issue a warning of an imminent ballistic missile attack.

Mobile phones across the Pacific islands received the emergency alert around 8:07 am and it was also transmitted by television and radio stations.

"In the minutes that followed, panic-stricken citizens called their families to say what they believed were their last words, and some even resorted to jumping into manholes to find shelter," FCC chairman Ajit Pai said in a statement accompanying the report.

The erroneous message came amid tensions with North Korea, which has claimed to have successfully tested ballistic missiles that could deliver atomic warheads to the United States.

It took the authorities 38 minutes to send out a message cancelling the false alert and the FCC report looked into why it took so long to do so.

The FCC investigation blamed the mistake on a combination of "human error and inadequate safeguards."