North Korea launched a suspected intermediate-range ballistic missile over Japan on Tuesday, authorities in Tokyo and Seoul said.

Although the launch was likely just a test, officials in the Japanese regions of Hokkaido and Aomori urged residents to take cover early on Tuesday morning.

"North Korea appears to have launched a missile," the Japanese government said in a rare activation of its J-Alert system. "Please evacuate into buildings or underground."

South Korean President Yoon Suk-yeol condemned Pyongyang's "reckless provocations" while Japan's prime minister, Fumio Kishida, called the missile launch "barbaric." No damage or injuries were reported.

Later on Tuesday, the South Korean Ministry of Unification said Pyongyang was unresponsive on the inter-Korea hotline used for negotiations between the two countries.

Missile launch 'threatened security of Japan'

The missile flew over Japan and landed in the Pacific Ocean some 3,000 kilometers (1900 miles) away from the archipelago, Japan's chief cabinet secretary, Hirokazu Matsuno, said.

Japanese and South Korean authorities said the missile traveled around 4,500 kilometers in total, and reached a speed of Mach 17.

"North Korea's series of actions, including its repeated ballistic missile launches, threatens the peace and security of Japan, the region, and the international community, and poses a serious challenge to the entire international community, including Japan," Matsuno added.

Japanese Defense Minister Yasukazu Hamada speculated that the missile could have been a Hwasong-12 rocket similar to the ones Pyongyang has tested in the past.

United States reaffirms 'ironclad' defense commitments

The White House called North Korea's missile launch "dangerous and reckless." The test was also condemned by the top US diplomat in East Asia and the US Indo-Pacific Command.

National security adviser Jake Sullivan consulted with his South Korean and Japanese counterparts on a "robust" international response, a spokesperson added.

Sullivan reaffirmed Washington's "ironclad commitment" to the defense of both Asian countries.

Tensions rising in the region

UN resolutions prohibit North Korea from testing any kind of ballistic missile. However, Tuesday's missile launch was the fifth such test in 10 days.

But unlike the other recent launches, Tuesday's test was the first time North Korea fired a missile over Japan since 2017 — a move that represents "a significant escalation over its recent provocations" according to Leif-Eric Easley, a professor at Ewha University in Seoul.

In August, the United States and South Korea kicked off large-scale joint military drills. North Korea views these exercises as an invasion rehearsal, however Seoul and Washington maintain they are defensive in nature.

Ankit Panda, an Asia-Pacific security expert with the US-based Carnegie Endowment for International Peace, said that firing over Japan allows North Korean scientists to test missiles under more realistic conditions.

"Compared to the usual highly lofted trajectory, this allows them to expose a long-range reentry vehicle to thermal loads and atmospheric reentry stresses that are more representative of the conditions they'd endure in real-world use," he said.

"Politically, it's complicated: the missile largely flies outside of the atmosphere when it's over Japan, but it's obviously distressing to the Japanese public to receive warnings of a possible incoming North Korean missile."