Students take cover under their desks during an evacuation drill in preparation for a North Korean missile attack, in Wajima, Ishikawa Prefecture, Japan, Aug. 30.
Students take cover under their desks during an evacuation drill in preparation for a North Korean missile attack, in Wajima, Ishikawa Prefecture, Japan, Aug. 30.

TSUBAME, Japan—For the second time in less than three weeks, loudspeakers across northern Japan on Friday alerted people that a North Korean missile was headed their way and told them they had minutes to seek cover. Smartphones buzzed Friday as the missile passed over the island of Hokkaido and landed in the Pacific Ocean.

Japan’s sophisticated emergency alert system, known as J-Alert, can get the word out within four minutes of a missile launch. But officials say training a nation of about 127 million people how to respond is the harder battle, since they would have about six minutes between the warning being sounded and the missile hitting.

“They just don’t know how to react to it,” said Hokuto Asano, a government official responsible for J-Alert. “I think the most important thing is to educate the people.”

 Hiroshi Sogo, 57, of Watabe, Japan, led his small village in a drill to prepare for a missile attack. Here, he points to possible hiding places.

The government began missile drills in some towns in March, and a weeklong Google ad campaign for J-Alert started Aug. 29, coincidentally the same day North Korea launched its first missile over Japan’s main islands since 2009.

In Watabe, a neighborhood of 250 people in the city of Tsubame near the coast of the Sea of Japan—in a part of the country facing North Korea— Hiroshi Sogo, 57, says he thinks an attack is unlikely but he is preparing nonetheless. A former serviceman in Japan’s military, he worked with the national government to carry out a missile preparedness drill in June, where they checked whether the town’s three sirens were in working order.

On Friday, they proved to be functioning just fine.

Mr. Sogo heard the sirens blare about 7 a.m. just after he woke. He said he told his wife and 27-year-old son to get together in the center of the house and pull bedding over themselves to take cover. “We stayed put until the announcement said [the] missile had passed over us,” he said.

Civilian preparedness would go only so far if a North Korean missile—not to mention a nuclear bomb—actually landed in a Japanese city. Pyongyang conducted its largest-ever nuclear test Sept. 3. Japan has other measures to try to protect its citizens. The Japanese ministry has sought funds to beef up the country’s existing missile-defense shield.

Looking west toward North Korea from Japan’s Sado Island as he leaned on his fishing boat, Masatoshi Iwasaki, 75, said the alert system wasn’t very effective because people often ignored the sirens and “we don’t know where we should hide.” A member of the small island’s disaster prevention force, he pointed to a radar base on the island that he worried could be a possible target for Pyongyang.

“I feel naked. I can’t protect myself if it happens,” he said.

Still, officials say even a few minutes is enough time for people to improve their chances of survival by moving to a place where there is less falling debris.

At the Watabe village drill in June, people plotted which evacuation route would be safest and where they would hide. Yoshinori Takeuchi, 70, a farmer and chief of the Watabe resident association, recalled hiding under a bridge, covering his eyes and mouth in line with government instructions.

His thoughts on the dangers of North Korea have shifted since the drill.

“In the beginning, I thought those things would never happen, but nowadays it’s more serious, so we’ve got to be prepared,” he said.

In the drill, everyone who was healthy enough to do so found cover in two minutes. A missile from North Korea would likely reach them in less than 10 minutes.

The J-Alert system began in 2007 to warn the public about threats—from tsunamis to heavy rain—and was widely adopted after the deadly Fukushima earthquake in 2011. Before 2017, it was used twice to warn about North Korean rocket launches, in 2009 and 2012.

“Japan has been at the forefront of early-warning technologies for a while,” said Daniel Aldrich, director of the security and resilience studies program at Northeastern University. “If you’re going to be stuck someplace when there is something bad happening, Japan is a very good place to be.”

In the U.S., the threat from North Korea is causing Hawaii to bring back an attack-warning siren that was discontinued in the 1980s. The tones will be blasted from about 400 sirens that were installed during World War II and are different from those the state uses for tsunami and hurricane warnings.

“We’ve been contacted by about a dozen states or so asking what we are doing here,” said Lt. Col. Charles Anthony, spokesman for the Hawaii state Department of Defense. The system will officially be ready on Nov. 1 but could be ready now if necessary, he said. “We wanted to make sure we got ahead of any capability the North Koreans may have.”