After North Korea launched an unidentified ballistic missile, Japan on Tuesday issued a warning urging some of its residents to go to shelters.

“North Korea appears to have launched a missile. Please evacuate to buildings or basements,” the government said in a warning released at 07:29 local time (00:29 CEST). The state broadcaster NHK reported that the warning applies to two northern regions of the country. The Japanese prime minister’s office tweeted that the missile, suspected to be a North Korean ballistic missile, may have passed over Japan. The Japanese coast guard also confirmed the launch of a suspected North Korean ballistic missile. Further details were not initially announced.

North Korea has repeatedly launched a ballistic missile in a matter of days. “North Korea launched an unidentified ballistic missile eastbound,” South Korea’s general staff said in a statement Tuesday.

A few days ago, North Korea fired ballistic missiles four times. A few hours before the third missile was launched, US Vice President Kamala Harris visited neighboring South Korea. Ashington and Seoul are close allies. Around 28,500 US soldiers are stationed in South Korea. UN resolutions prohibit North Korea from testing ballistic missiles of any range, which, depending on the design, can also carry a nuclear warhead. North Korea’s most recent missile tests are also seen by experts as a reaction to the recently held naval maneuvers by South Korean and US forces. The aircraft carrier USS Ronald Reagan also took part in the four-day naval exercises. It was the first deployment of a US aircraft carrier to South Korea in almost four years.

South Korea and the United States fear that Pyongyang could test nuclear weapons for the first time since 2017. According to South Korean and US officials, this could happen shortly after China’s upcoming party congress on Oct. 16.