The accident happened when one train crashed into the back of another, which had stopped on one of the system’s key routes because of mechanical problems.
Yonhap, the country’s news agency, reported that the fire department said the automatic controls which maintains space between trains most likely failed, citing city authorities.
Only minor injuries were reported however, although a train operator had to undergo surgery for a broken shoulder.
The incident occurred in the afternoon at the Eastern station of Sangwangsimni on Subway Line two, one of Seoul’s major transport arteries.
It had then promised an overhaul of the country’s safety system.
Passengers said the lights in the cars went out after the crash and 20 minutes went by without any announcements from the station.
This prompted many passengers to force open the doors and jump onto the track to escape.
Train service on the line was temporarily disrupted.
The Seoul subway system is one of the most heavily used in the world.
More than five million people use it every day.(dpa/NAN)