Initially, two children and two adults were taken to a hospital in critical condition, but ABC7 has learned that one of those adults, a 30-year-old woman, has died from her injuries.
According to authorities, that woman lived in a first-floor unit of the Lawndale-area building. The other adult critically injured, a man, also lived on the first floor.
Fire officials say one of the two injured children is 5-year-old girl who suffered 100 percent burns. The other child, a 9-year-old boy, suffered nearly 100 percent burns.
Authorities said the children were not likely to survive.
An 84-year-old woman and a woman in her 50s who live on the second floor were also injured. They were hospitalized and treated for smoke inhalation.
ABC7 is told the fire started at approximately 4 a.m. Neighbors said they saw and smelled smoke, heard a commotion and came outside.
"When I got there, there was person on the front lawn, and I saw the steam coming off of her body. It was a horrible scene," witness Ferdinand Miranda said.
Chicago police say they were told someone poured an accelerant on the victims and lit them. Police would not confirm those details.
"First arriving battalion chief sees number of victims. He requested an EMS Plan 1, which immediately brings five additional ambulances, brought in more manpower, transported six people. Four were red. Two were yellow," said Chicago Fire Department Dist. Chief Peter Van Dorpe.
Significant smoke and water damage to the building was visible.
Police remained on the scene hours after the incident.
Authorities say the home is being considered a crime scene.