Hawaii started monthly trials of an attack warning system Friday, in the first such test in the state since the end of the Cold War, days after North Korea's latest missile launch.

At 11:45 a.m., the Hawaii Emergency Management Agency, or HEMA, blared an "attack warning tone" from a WWII-era siren across the island state, signaling "impending nuclear missile attack."

"The possibility of attack today is very remote, but we do believe that it's important that we be proactive, that we plan and are prepared for every possibility moving forward," said Hawaii Gov. David Ige at a news conference Tuesday.

In what Ige calls "the new normal," every month Hawaiian residents and visitors, who number more than 7 million annually, will hear a 50-second "wailing" tone being tested in case of the "highly unlikely" event that North Korea launches an intercontinental ballistic missile at the U.S. state.

"We have to do something. We can't ignore it," said Vern Miyagi, administrator of the Hawaii Emergency Management Agency.

HEMA has spent the last two months ramping up awareness for the Attack Warning Tone and urging preparation for a nuclear weapon with town hall meetings and television appearances.

Japan estimated the explosive device detonated in a nuclear test by North Korea in September had a yield of about 160 kilotons, 10 times the force of the world's first atomic bomb dropped by the United States on Hiroshima in 1945.

The new "Attack Warning" siren follows the steady "Attention Alert" tone that indicates natural disasters such as hurricanes and tsunamis in the monthly statewide warning siren system test, which residents are accustomed to hearing.

At Waikiki Beach, tourists were undeterred from their sunbathing and swimming as the two siren tones sounded for two minutes.

"We were in the shop and didn't hear anything," said a woman in her 40s from Kanagawa, Japan. Several other visitors echoed that they did not hear the warning tones, nor did they know about the siren test. "They should work to put sirens on Waikiki Beach."

The attack warning tone was once an air-raid siren during the Cold War that prompted shelter-in-place exercises. Decades later and with North Korea recently re-designated as a state sponsor of terrorism, HEMA no longer has designated fallout shelters, including ones used during WWII and the Cold War which ended in the early 1990s, because of lack of funding.

There is not enough time to do much else besides "get inside, stay inside, and stay tuned" when the wailing siren is activated, officials say, with a missile from North Korea estimated to be able to reach Hawaii in around 20 minutes. There will be 10 to 13 minutes to shelter, according to HEMA, after activation of the siren and notifications over radio, television, and mobile devices.

Hawaii, which has shared nuclear preparedness information with Guam officials, is reportedly the first and only U.S. state taking measures to prepare for a North Korean attack. Various U.S. states, mostly in the western United States, have reached out to HEMA for information on Hawaii's preparedness program, said Miyagi.