Pyongyang fired at least three ballistic missiles towards the Sea of Japan, also known as the East Sea, the South Korean military said on Wednesday.
South Korean news agency, Yonhap, cited the Joint Chiefs of Staff (JCS) as saying that one missile flew toward the eastern South Korean island of Ulleungdo.
The missile then crashed into international waters in the Sea of Japan.
Another fell into the sea near the de facto maritime border with South Korea, while the third dropped into waters east of the city of Sokcho, Yonhap reported.
The agency cited the military as saying that Pyongyang fired some 10 missiles of various types.
Kyodo news agency cited the Japanese government as saying there were no reports of damage to aircraft or ships.
It added that the missiles may have flown on irregular trajectories.
No further details were initially released.
UN resolutions prohibited North Korea from testing ballistic missiles of any range, some of which were capable of carrying a nuclear warhead.
The situation on the Korean peninsula was currently very tense.
Nuclear-armed North Korea has conducted a string of missile tests in the past few weeks.
The government in Pyongyang has said in its own statements that the tests were intended to simulate the firing of tactical nuclear weapons at South Korean airfields.
A major joint air exercise involving some 140 aircraft from South Korea and 100 aircraft from the United States (U.S.) Air Force kicked off last Monday.
North Korea regularly accuses the U.S. of preparing an attack through its manoeuvres with South Korea, which both countries deny.
The U.S. has 28,500 soldiers stationed in South Korea.