CHICAGO (AP) _ A smoky fire broke out in a basement apartment early today, killing six people, including four children, and critically injuring one other child, authorities said.

The fire, which broke out about 2 a.m., was confined to a bedroom in the apartment and brought quickly under control, said Fire Department spokesman Jerry Lawrence said. The apartment did not have a smoke detector, he said.

The victims were asleep when the blaze started and died apparently of smoke inhalation, Lawrence said.

''Detectors ... might have provided the early warning necessary for the residents to escape, particularly considering how minor the fire was,'' he said.

Officials at five hospitals listed six dead in the fire - four children, ages 3 to 7, a woman about 25 years old and another woman in her late 20s. A 1-year-old was in critical condition at Children's Memorial Hospital, said spokeswoman Karen Shepherd.

On Thursday, a mother and three children died in a fire in Lena, Wis. Authorities said the woman threw her 3-year-old son to her husband through a second-story window, then died when she apparently went to get her other children.

The cause of the fire in Chicago was under investigation, Lawrence said, and authorities later indicated it may have been caused by an iron. The three- story brick building was being remodeled, he said.

''We recovered the iron from dead center,'' said Detective Robert Sherwin of the Chicago Police Bomb and Arson Squad.

Sherwin said the iron was lying against a mattress, which was smoldering and releasing large quantities of smoke.

''I saw about five (bodies), small babies. ... They had them in bags,'' said Samuel Williams, who lives two houses away. ''People were fainting when they were bringing out the bodies.''

''When I first saw it, there was flames and smoke,'' he said. ''But there was more smoke than anything else.''

He called the fire a ''terrible, terrible tragedy, a terrible thing to happen, young kids lost their lives before they even start living.''

The dead were identified as Angella Winfield, 28, and three of her children, Michael, 7, Latoya, about 5, and a girl, about 5 years old, whose name was given as Quitina or Quantina.

Ms. Winfield's 1-year-old daughter, Adora, was reported in critical condition at Children's Memorial Hospital.

Also dead were Reethan Boyd, 3, and his mother, Valerie Boyd, who was believed to be 28 years old, police said.

Ms. Winfield and her children had been staying with Ms. Boyd, Felix Winfield said.

Cora Hansbrough, who lives next door to the building, said her husband and landlady reported the fire. She said she was awakened by screams.

''I heard some people ... and they were saying those people won't come out and there's a fire in the basement,'' she said. ''I thought it was in the building where I am, but it wasn't.

''I just jumped up, running and screaming, 'Get up 3/8 Get up 3/8 There's a fire in the building 3/8'

''When we ... got downstairs, it was just a flame of smoke coming out, and you could just see a little blaze. Then we started screaming and going on and saying, 'Lord, is there anyone in there, is there anyone in there? And somebody said, 'There's got to be someone in there because there's a lot of kids in there.'''

After the fire was put out, she said: ''They brought a little child out. ... I saw them (firefighters) taking out two bodies on stretchers.''

Mrs. Hansbrough said her daughter made her leave the scene ''because I was taking it so hard. She made me leave because she was afraid I would have a heart attack to see those kids.''

The Oconto County, Wis., sheriff's department identified the victims of Thursday's blaze as Colleen Konitzer, 27, and three of her children: Travis, 8; Amanda, 4; and Melissa, 2.

John Konitzer, 44, the husband and father of the victims, was hospitalized, as was 3-year-old Benjamin and firefighter Al Schuettpeltz, 42, who was seriously injured when he fell from a ladder.

Sheriff Kenneth Woodworth said Konitzer told authorities his wife woke him around 7:15 a.m., screaming that the house was on fire. Mrs. Konitzer told her husband to go outside, and she tossed Benjamin through a window to him.

Konitzer said he put the child in his car. When he returned, his wife had disappeared, and flames prevented him from going back in the house.