Fire swept through two crowded trains and toxic fumes billowed down subway tunnels after a passenger reportedly ignited a milk carton or a small box filled with some kind of flammable material, possibly paint thinner, and threw it onto one of the trains.
The fire spread quickly, burning some victims beyond recognition while others, including passengers standing outside the trains on the subway platform, died of smoke inhalation.
Early reports indicate that doors of the trains may have failed to open, trapping passengers inside. A few trapped victims reportedly placed panicked phone calls to relatives before being overcome by fire, smoke and fumes.
A 56-year-old man with a reported history of mental illness is being held and questioned by law enforcement officials. Police have said the man has repeatedly threatened to burn down a hospital where he received treatment for a stroke in 2001. The man is also reportedly being treated for burns he suffered during the attack.
Survivors say passengers fought with the man as he tried to ignite the carton with a small lighter. The alleged attacker fled on foot but was arrested at a nearby hospital.
Daegu is the third largest city in South Korea with a population of 2.5 million.