North Korea fired at least 10 missiles of various types from its east and west coasts on Wednesday, South Korea's Ministry of National Defense said.
South Korea's Joint Chiefs of Staff (JCS) said the launches marked the first time a North Korean ballistic missile had landed near South Korean territorial waters - south of the northern boundary line - since the division of Korea.
The barrage of missile tests triggered an air raid warning on the South Korean island of Ulleungdo, located about 120 kilometers (75 miles) east of the Korean peninsula. JCS said a short-range ballistic missile fell in international waters 167 kilometers (104 miles) northwest of the island.
Wednesday's launch is North Korea's 29th this year, and comes after the United States and South Korea began previously scheduled military exercises called "Vigilant Storm" on Tuesday.
The maneuvers involve 240 aircraft and "thousands of military personnel" from both countries, according to the US Department of Defense.
US Secretary of Defense Lloyd Austin is due to meet his South Korean counterpart Lee Jong-sup at the Pentagon on Thursday.
Experts have previously told CNN that North Korean leader Kim Jong Un could send a message by deliberately showcasing the nation's arsenal during a time of intensified global conflict.
Last month, North Korean state media broke six months of silence on this year's round of missile tests, saying they were intended to demonstrate Pyongyang's willingness to fire tactical nuclear warheads at targets. potential targets in the South.
The latest tests also come after the head of the United Nations nuclear watchdog warned last week that Pyongyang could be preparing for a nuclear test.
“We are following this very, very closely. We hope that doesn't happen, but the indications are unfortunately pointing in another direction,” International Atomic Energy Agency chief Rafael Grossi said last Thursday.
Speaking on Wednesday, Japanese Prime Minister Fumio Kishida told reporters that North Korea was launching missiles with "unprecedented frequency".
Kishida also called for a National Security Council meeting to be held as soon as possible due to rising tensions on the Korean Peninsula.
Earlier on Wednesday, Japanese Defense Minister Yaukazu Hamada said North Korea had fired at least two missiles and both would have fallen outside Japan's exclusive economic zone (EEZ).
No damage to aircraft or ships has been reported so far, and it is possible that the ballistic missiles flew on an irregular path, he added.