The accident occurred at about 11 a.m. in a run-down two-story residential unit located in Cheonho, in the eastern Gangdong district, police and firefighters said.
The blaze, believed to have started from the first floor, gutted down the interior as it was put out completely in about 16 minutes, they said.
Firefighters rescued six women from the second floor. One of them died shortly after, and five others were sent to a hospital. Three of them sustained serious injuries and are undergoing treatment, but a 46-year-old woman died from her injuries, police said. One suffered minor injuries.
The first deceased victim, in her 50s, was the brothel owner, police said. She is believed to have shouted out for help and let the others escape ahead of her. The survivors may not have made it out of the building if it weren't for the owner, the police said.
Witnesses told police that they heard a bang before they saw the blaze.
A restaurant owner said he ran down with a fire extinguisher in his hand as soon as he heard somebody say "Fire!"
"But the windows were broken and the blaze had gotten too big for me to put it out on my own," the man said.
Police are investigating to figure out the exact cause of the fire.
The unit was one of the oldest buildings in the neighborhood -- at least 50 years -- and was set to be demolished in three days as part of a redevelopment project. Source from the Yonhap.