CHICAGO (CBS) — A woman was killed and a man was critically injured in an apartment fire early Wednesday in the Humboldt Park neighborhood.

When firefighters arrived at the scene in the 1000 block of North Hamlin Avenue shortly before 1 a.m.

READ MORE: 'John Doe' Who Accused Former Blackhawks Video Coach Brad Aldrich Of Sexual Abuse Identifies Himself As Kyle Beach

Witnesses heard explosions and windows breaking, and saw heavy smoke and fire coming from the second floor of the building, which has three apartments above a corner grocery store.

“As the Fire Department was coming around the alley, I seen somebody up in the window, and I was screaming to them, ‘There’s somebody in the building still. There’s somebody up there.’ So I could hear Fire Department, like,‘Where? Where?’ and I’m like, ‘In the window,” so all of a sudden they just started running up to the roof and breaking all the windows,” Jose Cedeno said.

Crews found a 72-year-old woman on second floor. She was taken to Norwegian American Hospital, where she was pronounced dead. The Fire Department initially said the woman was in her mid 40s, but later said she was 72.

A 74-year-old man also was found on the second floor, suffering from smoke inhalation. He was rushed to Norwegian in serious to critical condition, but his condition had stabilized by later Wednesday morning, and investigators were questioning him about what might have started the fire.

READ MORE: Macy's Holding Hiring Event In Minooka, Illinois Thursday

“We found heavy fire on the second floor. During a primary search, Tower Ladder 14 and Truck 36 found two victims,” Fire Department Deputy District Chief Jack Nagle said.

Nagle said smoke detectors were found in the hallway and in the rear apartments, but some of them were not working.

The American Red Cross was providing assistance to at least seven people who were left homeless as a result of the fire, helping them find temporary housing.

MORE NEWS: Man Hit With Broken Bottle During Argument On CTA Blue Line Train Near Chicago Avenue

The cause of the fire was under investigation, but officials said it appeared accidental.