Seoul's joint chiefs of staff said in a statement that the "unidentified projectile" was launched into the Sea of Japan, known as the East Sea in Korea.

No further details of the device type, or how many were fired in total, were immediately available.

The nuclear-armed North is banned from developing ballistic missiles under UN Security Council resolutions.

But it has made rapid progress in its capabilities under leader Kim Jong Un, testing missiles capable of reaching the entire continental United States as tensions mounted in 2017.

Thursday's incident comes after Pyongyang fired two short-range, non-ballistic missiles in a westerly direction towards China at the weekend.

That followed a visit to the region by US Secretary of State Antony Blinken and Defense Secretary Lloyd Austin to discuss alliance and security issues in the region, with the North seen as a central threat.