Two aircraft of South Korea's air force have collided in mid-air during a training exercise, killing three pilots, with a fourth missing in the rare incident, authorities say.
More than 30 firefighters and rescuers have begun a search at the crash site, the Yonhap news agency said, citing fire officials.
The crash happened about 6km south of the KT-1 airplanes' base in the southeastern city of Sacheon, at about 1.37pm on Friday, the air force said.
"Despite their attempts at an emergency escape, three pilots died and one remains missing," it said in a statement, adding that it had formed a team to determine the cause of the accident and damage.
The KT-1 is a single-engine basic trainer and light attack aircraft jointly built by the state-run Agency for Defence Development and a contractor, Korea Aerospace Industries.Â