A fire in a bus terminal in Goyang, Gyeonggi Province on Monday morning left seven people dead and more than 50 injured.
The fire was extinguished within 28 minutes, but sprinklers and fire-resistant shutters between the floors designed to block toxic gas did not work properly, causing many casualties.
The fire was started by sparks from gas pipe welding work at a shop on the first basement level, police said.
Soon afterwards, the fire spread to the ceiling and nearby combustible materials, producing toxic smoke that billowed upward, firefighters said.
Most of the casualties were terminal staff, police and firefighters said. All of them appeared to have died from inhaling toxic smoke. The injured were taken to nearby hospitals.
At the time, about 700 people were inside the building, which beside the bus terminal contains a cinema and a shopping mall.
Most evacuated when they heard the sound of sirens.
A firefighter said several fire-resistant shutters did not work properly. For some reason the sprinklers on the ground floor were not activated either.