South Korea's air force said that two KT-1 trainer jets collided with each other in mid-air.
According to Yonhap News Agency, the planes crashed in a rice paddy, leaving three pilots dead and another seriously injured. Over 30 firefighters and two helicopters are at the site of the crash, according to reports.
Authorities are investigating the cause of the accident.
The KT-1 training aircraft was developed by KAI for the South Korean Air Force. This is the first aircraft for military purposes to have been completely produced in South Korea.