South Korea's military said it scrambled fighter jets after detecting about 180 North Korean warplanes flying north of the military border over four hours on Friday.
The North Korean aircraft flew north of the so-called tactical measure line, drawn to up 20 kilometres (12 miles) north of the Military Demarcation Line (MDL), South Korea's military said in a statement.
South Korea scrambled 80 aircraft, including, F-35A stealth fighters, in response. About 240 aircraft participating in the Vigilant Storm air exercises with the United States continued the drills, the military said.
A flight of 10 North Korean warplanes made similar maneuvers last month, prompting South Korea to scramble jets.
The maneuvers came after North Korea fired more than 80 rounds of artillery into the sea overnight, and the launch of multiple missiles into the sea on Thursday, including a possible failed intercontinental ballistic missile (ICBM).
The launches prompted the United States and South Korea to extend air drills that have angered Pyongyang.
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