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, and South Korea responded with missile launches of its own, officials said.

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 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 26 kilometres south of the NLL, 57 kilometres from the South Korean city of Sokcho, on the east coast, and 167 kilometres from the island of Ulleung, where air raid warnings were issued.