There were no reported fatalities on the ground, but one high school student was injured by flying debris when the helicopter crashed shortly before 11:00 am (0200 GMT), narrowly missing nearby apartment blocks in the southern city.
Yonhap news agency said the crew were returning from a mission to help in the search for missing victims of April's ferry disaster off the southern coast.
"Five people were on board and all are presumed dead," local fire chief Moon Ki-Shik told reporters at the scene, adding that the cause of the crash was not immediately clear.
Television footage showed the wreckage burning by the side of a main road.
The aircraft was identified as a Eurocopter Dauphin 2, a twin-engine chopper produced by Airbus Helicopters. - AFP