The email, with the subject line "In the event of a nuclear attack", provided information about emergency sirens and sheltering in place, according to CBS-affiliate Hawaii News Now.
A University of Hawaii spokesman is apologizing for "needless attention" from an email sent to faculty, staff and students systemwide Monday with the subject line, "In the event of a nuclear attack".
"It may sound insane to outsiders to fire missiles from a place he wants to develop economically, but that's how Kim Jong Un runs his country", said Mr Lim Eul Chul, an expert on the North Korean economy at Kyungnam University in South Korea.
Hawaii officials were discussing how to brace residents for a possible atomic attack, The Washington Post reported.
It went on to say state and federal agencies are now providing information about potential nuclear threats and advising what to do should a nuclear attack and resulting radiation emergency occurs.
"It could be the most powerful detonation of an H-bomb in the Pacific", Foreign Minister Ri Yong Ho told reporters. He said at the least, he should have worded it, "In the event of an unlikely nuclear attack". "Kim Jong Un knows that he can only control society and guarantee his long leadership if his role and influence in the economy is increased", said Mr Thae. The threat from North Korea has joined the list of dangers being planned for in Hawaii.
Once a missile is launched from North Korea, there will be less than 20 minutes warning, Miyagi said.
In September, the Hermit Kingdom successfully conducted its sixth nuclear test, with the regime claiming it detonated its first hydrogen bomb. President Donald Trump and North Korean leader Kim Jong Un have engaged in a war of words for weeks.
North Korea has repeatedly threatened to strike the USA mainland, even vowing to strike the US territory of Guam with four medium-range ballistic missiles in August, though Pyongyang later backed away from the brink.