According to witnesses, one train was hit from the rear by another incoming train while leaving Sangwangsimni station in the east of Seoul.[4] Another witness said many passengers forced the doors open and escaped onto the tracks after ignoring the onboard announcement which told them to stay inside the cars.[8] The decision by many passengers to ignore instructions was likely due to distrust in authorities after the Sinking of MV Sewol and Daegu subway fire, where instructions to remain onboard resulted in several fatalities.[9]
YTN television reported one subway car was derailed, so passengers had to walk a short distance along the tracks to the station. A government emergency official said that many passengers were injured as they jumped from the subway cars onto the tracks.[4] Yonhap said the train stopped due to mechanical problems after the second train ran into the back of it.[8] It also said that ‘a failure in the moving train’s automatic distance control system’ may have been the cause, while officials were still investigating the accident.