Two South Korean air force planes collided in mid-air on Friday during a training exercise, killing four pilots, authorities said.

According to Reuters, a total of 130 troops, 95 police officers and 60 firefighters as well as three helicopters have begun a search at the crash site, the Yonhap news agency said, citing local government officials.

The crash happened about 6 km (3.7 miles) south of the KT-1 airplane base in the southeastern city of Sacheon, at about 1:37 p.m.(0437 GMT), the air force said.

The crash site is located in a largely agricultural area, and photos published by Yonhap showed smoke rising from a mountain, and one car shattered by fragments of the aircraft while parked in front of a farmhouse.

The KT-1 is a single-engine basic trainer and light attack aircraft jointly built by the state-run Agency for Defense Development and a contractor, Korea Aerospace Industries.

“Despite their attempts at an emergency escape … all of the two student pilots and two flight instructors aboard the two planes died,” it said in a statement.

President Moon Jae-in offered condolences to the victims’ families.

The air force said there were no civilian casualties but had formed a team to determine the cause of the accident and damage, including on the resident community.