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

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 south-eastern city of Sacheon, at about 1:37 p.m.(0437 GMT), the air force said.

"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.

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 Defence Development and a contractor, Korea Aerospace Industries.