South Korea's military on Wednesday denounced North Korea's launch of its first missile into an area close to the South's territorial waters since the division of the peninsula more than seven decades ago, calling it an "intolerable" act.

Earlier in the day, the North launched at least three short-range ballistic missiles into the East Sea, one of which flew across its de facto maritime border with South Korea, according to the South's military.

The Joint Chiefs of Staff said the missile firing from a site in or around the North's eastern coastal city of Wonsan was detected at around 8:51 a.m.

"North Korea's missile launch, which marks the first time since the division of the peninsula that has landed near our territorial waters south of the Northern Limit Line, is very rare and intolerable," the JCS said in a press release.

"Our military vowed to respond firmly to this (provocation)," it added. (Yonhap)