Hawaii is set to reinstate a World War II-style missile warning system from December 1 amid fears of a nuclear attack by North Korea, Reuters reported.

The warning sirens have not been used in the last 30 years, since the Cold War. The air siren will sound for 60 seconds from around 400 locations across the islands, and will be repeated on the first working day of each month, officials said.

Public service announcements in Hawaii will urge the residents to “get inside, stay inside and stay tuned” if they hear the warning. “Emergency preparedness is knowing what to expect and what to do for all hazards,” Hawaii Emergency Management Agency Chief Vern Miyagi said, but did not specifically mention North Korea.

The sirens are being reactivated in light of the recent test launches of intercontinental ballistic missiles from North Korea, which may reach the state, said Hawaii Emergency Management Agency spokesperson Arlina Agbayani.

A single 150-kilotonne weapon detonated over Pearl Harbour on the main island of Oahu would be “expected to kill 18,000 people outright, and leave 50,000 to 1,20,000 others injured”, said another spokesperson of the agency, Richard Rapoza.

United States President Donald Trump has warned North Korea a number of times against boosting its nuclear weapons programme this year. In July, Pyongyang twice launched a long-range missile that could potentially reach the US mainland. In September, it conducted its sixth and most powerful atomic bomb test yet.