North Korea fired a ballistic missile of intermediate range or longer on Thursday, South Korea and Japan said, prompting an alert for residents in Japan’s northern island of Hokkaido to take cover.

Japanese authorities later retracted the warning, saying the country’s J-Alert emergency warning system had made an erroneous prediction the missile would fall near the island.

The missile flew about 1,000 km (620 miles), South Korea‘s military said, calling it a “grave provocation”. The apogee, or maximum altitude of the missile, has not been disclosed.

Prime Minister Fumio Kishida of Japan said his government would hold a National Security Council meeting on the launch.

Japan’s defence minister, Yasukazu Hamada, said the missile appeared to have been fired eastward at a high angle. He said the missile did not fall in Japanese territory, and that the defence ministry was analysing the launch for more details.

Japan’s coast guard said the projectile had fallen in the sea to the east of North Korea. Hamada said he could not confirm whether the missile flew over Japan’s exclusive economic zone.

There have been problems with J-Alert before.

In October, an evacuation warning was issued when a missile overflew Japan but it came so late most people were not aware of it until the projectile had fallen into the Pacific.

A month later, a warning was erroneously issued saying a missile had overflown Japan.

On Thursday, a student told Japanese broadcaster NHK that the alert caused momentary alarm at a train station in Hokkaido.

“For a second in the train there was panic, but a station worker said to calm down, and people did,” said the man, whom NHK did not name.

The launch came days after North Korean leader Kim Jong Un called for strengthening the country’s war deterrence in a “more practical and offensive” manner to counter Pyongyang called moves of aggression by the United States.

The missile was fired at 7:23 a.m. (2223 GMT on Wednesday) from near Pyongyang, South Korea‘s Joint Chiefs of Staff said.

The South Korean military said it was on high alert and coordinating closely with the United States.

North Korea has criticised a recent series of joint military exercises between the U.S. and South Korea as escalating tensions, stepping up its weapons tests in recent months.