The blaze is believed to have broken out on the third floor of the three-story building at around 5 a.m. in the center of the capital, according to the firefighters. It was extinguished at 7 a.m.
"We've got a witness statement that the fire started at a room near the entrance to the third floor," a fire official said. "People inside had great difficulty evacuating because the exit was blocked by the blaze."
About 50 residents were at the accommodation -- commonly referred to as a "goshiwon" in Korean -- which occupied the second and third floors of the building. Most of the residents are day laborers, and those killed or injured were aged between their 40s and 60s, officials said.
Officials said the number of casualties could rise.
The aged building had no sprinkler, but it was equipped with other emergency equipment, such as an emergency bell, an emergency exit and an emergency descending device.
"Victims failed to use the descending device. They might have panicked in the fire," an official said.
Police and fire officials said they will look into what exactly caused the fire and if the fire detector installed in each room worked properly.
"We will secure CCTV footage and witnesses to see if there's any suspicions of crime," a police official said.
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