According to the Yonhap news agency, citing the South Korean military, Pyongyang fired an unidentified projectile on Friday. The projectile was launched off the east coast of North Korea toward the Sea of Japan.
The Japanese Border Guard has suggested the projectile could be a ballistic missile. The coast guard also issued a warning at 14:55 local time (05:55 GMT), urging vessels currently at sea to be careful and stay away from the object if it falls into the water.
The launch was reported after Pyongyang held several hypersonic missile tests in January, announcing that the projectile had reached a speed of Mach 10 or more than 7,600 miles per hour.
The previous missile launches prompted sanctions against North Korea by the US. In response, Pyongyang promised to boost its action if Washington doesn't abandon its "confrontational stance".