This included one projectile that flew close to South Korea’s Ulleung island before hitting waters off its east coast.
The barrage triggered a response from Seoul, which fired off three of its own missiles as tensions on the Korean peninsula grow.
The show of force comes as Washington and Seoul are carrying out joint “Vigilant Storm” air force drills in South Korea.
This is the first time both Korean nations have fired missiles which have landed in each other's coastal territory, with the South Korean military warning it represented a “highly unprecedented” escalation.
The launch of 23 missiles is a record number of daily missile tests by North Korea, experts claimed.
Air raid sirens were activated to warn South Korean residents on Ulleung island to take cover, officials from Seoul’s defence ministry said. Local media reports said the sirens blared for around three minutes, though people were not initially aware of what they were supposed to signify.
The first barrage included at least three-short range ballistic missiles and seven missiles of other types which were not immediately identified, South Korean officials said.
“The ROK [South Korean] military, at around 8.51am, detected three short-range ballistic missiles that North Korea fired from Kangwon Province’s Wonsan region, and one of these fell in international waters of the East Sea, south of the Northern Limit Line [NLL],” said an official statement.
The NLL is a line generally recognised as the sea border between the two Koreas, though North Korea has not formally acknowledged this.
Another missile was confirmed to have been fired within minutes. Around 20 minutes later, at 9.12am, the South Korean military said North Korea fired 10 more missiles, including SRBMs and surface-to-air missiles.
Four hours later, North Korea fired around 100 artillery shells in a breach of the inter-Korean military agreement with Seoul and dropped them into the inter-Korean maritime on Wednesday afternoon which landed north of NLL.
The raining of missiles into the eastern waters continued later in the afternoon around 4.43pm when Japan said North Korea fired another likely ballistic missile.
Two hours later, the South Korean military confirmed its neighbour had fired six more surface-to-air missiles into the East and West Seas – taking the total number of projectiles fired by North Korea to 23.
North Korea has not yet commented, but has warned it would take action if the US and South Korea went ahead with joint military exercises.
South Korea responded to the missiles fired by its neighbour with its own test launch involving at least three air-to-ground missiles, the military said.
The “precision air-to-surface missiles” reportedly fell a similar distance into North Korean waters, north of the NLL, to the North Korean missile that landed near Ulleung.
South Korea said it deployed a US-made “stand-off” precision attack weapon — an AGM-84H/K SLAM-ER — that can fly for up to 270km (170 miles) with a 360kg (800-pound) warhead, in the tests.
South Korean president Yoon Suk-yeol’s office had said it would deliver a “swift and firm response” to ensure the North “pays the price for provocation”.
“North Korea‘s provocation today was an effective act of territorial encroachment by a missile intruding the NLL for the first time since [the two Koreas’] division,” Mr Yoon’s office said.
Wednesday’s launch is one of the largest single missile bombardments fired by Pyongyang since 2010.
It takes the total number of missiles fired by Pyongyang this year to well over 60 – including nearly 50 ballistic missiles. Most of these were fired in the direction of the East Sea.
Additionally, the country also fired more than 100 rounds of artillery from its east coast into a military buffer zone established in an agreement with Seoul, South Korea’s military said.
The launches were also reported by Japan, but it did not immediately confirm a tally of missiles fired.
“North Korea has launched a suspected ballistic missile. More updates to follow,” Japan’s prime minister’s office said, issuing directions to its units to prepare for contingencies.
Seoul’s army lieutenant general Kang-Shin-chul said the launches on Wednesday were “highly unprecedented and can never be tolerated”. “Our military declares we will respond firmly to this,” the top military official said.
As a result of increased tensions in the Korean peninsula, South Korea has shut some air routes over the sea between North Korea and Japan till Thursday morning, its ministry of land, infrastructure and transport said on Wednesday.
“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.
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