North Korea has fired at least 17 missiles into the sea, including one that landed less than 60km off South Korea's coast, prompting South Korea to issue rare air raid warnings and launch missiles in response.
It was the first time a ballistic missile had landed near the South's waters, and the most missiles fired by the North in a single day.
The missile landed outside of South Korea's territorial waters, but south of the Northern Limit Line (NLL), a disputed inter-Korean maritime border in what South Korean President Yoon Suk-yeol called an "effective act of territorial encroachment."
South Korean warplanes fired three air-to-ground missiles into the sea north across the NLL in response, the South's military said.
The South's launches came after Yoon's office vowed a "swift and firm response" so North Korea "pays the price for provocation".
The North Korean weapon was one of three short-range ballistic missiles fired from the North Korean coastal area of Wonsan into the sea, South Korea's Joint Chiefs of Staff (JCS) said. The JCS later said as many as 14 other missiles of various types had been fired from North Korea's east and west coasts.
The JCS said at least one of the missiles landed 26km south of the NLL, 57km from the South Korean city of Sokcho, on the east coast, and 167km from the island of Ulleung, where air raid warnings were issued.
"We heard the siren at around 8:55 am and all of us in the building went down to the evacuation place in the basement," an Ulleung county official told Reuters. "We stayed there until we came upstairs at around 9:15 after hearing that the projectile fell into the high seas."
The North also fired more than 100 rounds of artillery from its east coast into a military buffer zone established in a military agreement with the South, South Korea's military said.
The firing violates the 2018 agreement, the JCS said.
Nuclear-armed North Korea has tested a record number of missiles this year, and officials in Seoul and Washington say the North has completed technical preparations to conduct a nuclear weapon test for the first time since 2017.
The launches came just hours after Pyongyang demanded that the United States and South Korea stop large-scale military exercises."
The US and South Korea began one of their largest combined military air drills on Monday. Dubbed Vigilant Storm, the exercises involve hundreds of warplanes from both sides staging mock attacks 24 hours a day.
North Korea had said that a recent flurry of launches were in response to allied drills.
Pak Jong Chon, secretary of the Central Committee of North Korea's ruling Workers' Party, said in a statement on Wednesday that the number of warplanes involved in Vigilant Storm proved the exercise was "aggressive and provocative" and specifically targeted North Korea. He said even its name imitated the US-led Operation Desert Storm against Iraq in the 1990s.
On Tuesday US State Department spokesperson Ned Price said that the drills were "purely defensive in nature" and that the United States had made clear to North Korea that it harboured no hostile intent towards the country.
Price added that the US and its allies had also made clear that there would be "profound costs and profound consequences" if North Korea resumed nuclear testing, which would be a "dangerous, destabilising step". He did not elaborate on the consequences.
In a phone call with U.S. Secretary of State Antony Blinken, South Korean Foreign Minister Park Jin called the North Korean missile launches a "grave act of military provocation".
Japan defence minister Yasukazu Hamada said North Korea's actions threaten the peace and stability of Japan, the wider region, as well as the broader international community, and are utterly unacceptable.