A part of the train's electrical insulation device was damaged and triggered the explosion at a station in Gunpo city just south of Seoul, local emergency official Yoo Hyung-gi said. He said operations later resumed at the station.

The incident came as South Korean media ramped up their focus on allegations of widespread safety negligence in the country following a ferry disaster that left more than 300 people dead or missing last month. There is suspicion that the ferry set off with far more cargo than it could safely carry and that crew members abandoned passengers in need.

Earlier this month, a subway train plowed into the back of another train at a station in Seoul, inflicting mostly minor injuries to more than 240 people.

The series of incidents threw a spotlight on the infrastructure and safety as South Korea rose rapidly from the destruction of the 1950-53 Korean War to Asia's fourth biggest economy.