A North Korean ballistic missile landed less than 60 kilometres off South Korea's coast on Wednesday, the first time an apparent test had landed near the South's waters, prompting South Korea to issue rare air raid warnings and launch missiles in protest.

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.

An official said the weapons used included an AGM-84H/K SLAM-ER, which is a US-made “stand-off” precision attack weapon that can fly for up to 270km with a 360 kilogrammes warhead.

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 10 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 8:55am 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 9:15am after hearing that the projectile fell into the high seas.”

A resident on the southern part of the island said they received no warnings.

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, saying such “military rashness and provocation can be no longer tolerated.”

Despite Yoon's declaring a national week of mourning after more than 150 people were killed in a weekend crowd surge in Seoul, the United States 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.

Major military drills

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.

“The hostile forces' inordinate moves for military confrontation have created a grave situation on the Korean peninsula,” Pak said in a statement carried by state news agency KCNA.

On Tuesday in Washington, US State Department spokesperson Ned Price responded to North Korea's warnings about a “powerful” response to the drills by saying that Pyongyang appeared to be “reaching for another pretext for provocations it has already undertaken, potentially for provocations that it might be planning to take in the coming days or coming weeks.”

He said that the drills were “purely defensive in nature” and that the US 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 US Secretary of State Antony Blinken, Foreign Minister Park Jin called the North Korean missile launch “unprecedented” and a “grave act of military provocation”. The two officials condemned the launch and agreed to cooperate against North Korean threats, Park's office said in a statement.

Launching missiles in 'new ways'

South Korea's Ministry of Land, Infrastructure and Transport said that because of the launches, some air routes over the sea between North Korea and Japan would be closed until Thursday morning.

A spokesman for the South Korean military said authorities were analysing the launches to see whether the missiles' flight paths were intentional or whether one had gone off course.

Japan Defence Minister Yasukazu Hamada said the government believed at least two ballistic missiles had been launched from North Korea, one flying east and another southeast.

The first flew 150km to a maximum altitude of approximately 150km, while the second covered a range of 200km to a maximum altitude of 100km, he said to reporters in Tokyo on Wednesday morning.

It was the first time a North Korean ballistic missile had landed near South Korean waters, JCS said.

“Our military can never tolerate this kind of North Korea's provocative act, and will strictly and firmly respond under close South Korea-US cooperation,” JCS said in a news release.

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, Hamada said.

“North Korea has been repeatedly launching missiles at an unprecedented rate, in new ways that we have not seen before,” he said.

Japan has lodged a complaint and protested the actions via diplomatic channels in Beijing, he added.