The latest launch comes just three days after Pyongyang last fired a missile, as warnings grow that it may conduct a nuclear test.

"North Korea fires at least one projectile into East Sea," Seoul's Joint Chiefs of Staff said, referring to the Sea of Japan.

Japan's coast guard, citing information from its Defence Ministry, said that North Korea had launched an object "likely to be a ballistic missile," and warned its vessels to be aware.

The launch is likely the nuclear-armed country's 15th weapons test so far this year.

On Wednesday, North Korea test-fired what Seoul and Tokyo said was a ballistic missile, although Pyongyang's state media -- which typically report on weapons tests -- did not comment on the event.

Despite biting international sanctions over its weapons programs, North Korea has dramatically ramped up testing this year while ignoring the United States' offers of talks.

The Saturday test comes just a few days before South Korea's new hawkish President Yoon Suk-yeol is inaugurated on Tuesday.