North Korea has fired a ballistic missile, South Korea's military said on Wednesday. (Representational)
North Korea fired at least 17 missiles Wednesday, including one that landed close to South Korea's waters in what President Yoon Suk-yeol said was "effectively a territorial invasion".
It also fired an artillery barrage into a maritime "buffer zone", in what experts said was part of an "aggressive and threatening" response by Pyongyang to the large-scale joint air drills the United States and South Korea are currently conducting.
One short-range ballistic missile crossed the Northern Limit Line, the de facto maritime border, prompting a rare warning for residents on the island of Ulleungdo to seek shelter in bunkers.
Seoul's military said it was the "first time since the peninsula was divided" at the end of Korean War hostilities in 1953 that a North Korean missile had landed so close to the South's territorial waters.
"President Yoon pointed out today that North Korea's provocation is an effective territorial invasion by a missile," his office said in a statement.
One of the missiles landed in waters just 57 kilometres (35 miles) east of the mainland, the military said, adding it was a "very rare and intolerable" incident.
Pyongyang fired a total of seven short-range ballistic missiles and 10 other missiles, Seoul's military said.
North Korea also conducted an artillery barrage, firing into a maritime "buffer-zone" set up in 2018 in a bid to reduce tensions between the two countries, during an ill-fated bout of diplomacy.
The huge volley of launches were "provocations against South Korea," said Go Myong-hyun, a researcher at the Asan Institute for Policy Studies.
"I wouldn't be surprised if they lead up to a nuclear test," he added.
South Korea, for its part, said it had fired three air-to-ground missiles into the sea towards the north of the two countries' maritime boundary.
President Yoon called a meeting of the National Security Council, ordering "swift and stern measures so that North Korea's provocations pay a clear price".
South Korea closed some air routes over the East Sea, also known as the Sea of Japan, advising local airlines to detour to "ensure passenger safety in the routes to the United States and Japan".
Vigilant Storm
Pyongyang's latest launch comes as Seoul and Washington stage their largest-ever joint air drills, dubbed "Vigilant Storm", which involve hundreds of warplanes from both sides.
Pak Jong Chon, a high-ranking official in North Korea, said the drills were aggressive and provocative, according to a report in state media Wednesday.
Pak said the name of the exercises harks back to Operation Desert Storm, the US-led military assault on Iraq in 1990-1991 after it invaded Kuwait.
"If the US and South Korea attempt to use armed forces against the (Democratic People's Republic of Korea) without any fear, the special means of the DPRK's armed forces will carry out their strategic mission without delay," he said.
"The US and South Korea will have to face a terrible case and pay the most horrible price in history."
Close to S Korea
One of the missiles on Wednesday landed in waters just 57 kilometers (35 miles) east of the South Korean mainland, the military said.
"In protest of the joint US-South Korea drill, Pyongyang seems to have staged the most aggressive and threatening armed demonstration against the South since 2010," Cheong Seong-chang, a researcher at the Sejong Institute told AFP.
In March 2010, a North Korean submarine torpedoed the South Korean naval vessel Cheonan, killing 46 sailors including 16 who were on their mandatory military service.
In November the same year, the North shelled a South Korean border island, killing two marines -- both of them young conscripts.
"It is now a dangerous and unstable situation that could lead to armed conflicts," he added.
The test follows a recent blitz of launches, including what the North said were tactical nuke drills, that Washington and Seoul have repeatedly warned could culminate in another nuclear test -- which would be Pyongyang's seventh.
The Vigilant Storm air drills were preceded by 12 days of amphibious naval exercises.
"As far as I can remember, North Korea has never made such a provocation when South Korea and the US were holding their joint drills," Park Won-gon, a professor at Ewha University, told AFP.
"Pyongyang seems to have completed its most powerful deterrent. This is a serious threat. The North also seems confident in their nuclear capabilities."
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