Authorities yesterday faced anger and demands for answers after a false alarm about an incoming ballistic missile caused panic in Hawaii, a Pacific archipelago already on edge over fears of a North Korean attack.

The notification was sent out just after 8:00 am (1800 GMT) on Saturday, lighting up phones with a disturbing alert urging people to "seek immediate shelter."

Emergency management officials later admitted "the wrong button was pushed" during a shift change.

But it took nearly 40 minutes for a corrected message to be issued -- with Hawaii's governor saying there was no automatic way to cancel the false alarm, meaning it had to be done manually.

The Federal Communications Commission (FCC), which is responsible for standards, procedures and testing protocols for the Emergency Alert System that delivered the false alert, promised a "full investigation".

The alert, which read "BALLISTIC MISSILE THREAT INBOUND TO HAWAII. SEEK IMMEDIATE SHELTER. THIS IS NOT A DRILL", sparked panic, with people rushing for safety whether in a bathtub, a basement, a manhole or cowering under mattresses.

And after it was declared a false alarm and the panic had subsided, there was anger, with many asking how such an error could have happened.

TERRIFIED AND ANGRY

"Everyone in America needs to understand that if you had to go through this, you would be as angry as I am," Representative Tulsi Gabbard of Hawaii wrote on social media.

"We're terrified and angry. Called my parents. Called my sister. Husband and I were shaking, verge of tears. Waited 40 minutes for a correction. No confidence in this emergency alert system," photographer Aislinn Victoria said on Twitter.

Adventurer Alison Teal called it "the worst moment of my life."