Chicago fire officials said two other people were also hurt in the blaze, and one died.
The fire broke out just after 2 a.m. in the basement of a two-floor apartment building in the 3100-block of North Marmora Avenue, right next to St. Ferdinand Church in Belmont Central, Chicago police said.
Chicago fire officials said the victims besides the firefighter who were injured included two men and a woman, who was taken to Loyola University Medical Center. All three suffered burns and were also critically injured. They were trapped in the basement unit and unable to escape without injury.
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One was pronounced dead at the hospital, officials said, though they did not specify who.
"My dog started barking," said Fernando Balbuena, resident. "My wife woke up and started smelling burning something."
The property owner said his three tenants are in their thirties.
The firefighter, who had just celebrated his first anniversary with the department and is relatively young, was taken to Community First Hospital, where other firefighters began to gather early Thursday morning.
"This is heartbreaking, to be standing here this morning for this right before the holidays," said Chicago Fire Commissioner Annette Nance-Holt.
He was later transferred to Loyola Hospital in Maywood, which has a unit that specializes in treating severe burn victims.
Chicago fire officials said he needed to be intubated because his throat is severely burned.
A man who lives in the building said his dog woke him up and so did the strong smell of smoke. Fire crews got there rather quickly, with a fire station just five minutes away.
The cause of the fire is still being investigated, but the blaze was put out about 3:30 a.m.
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The building appeared to be a total loss, and the high winds made things more difficult for crews.
Fire officials could not say if smoke detectors were working at the time.
Nance-Holt asked the community to pray for those injured during a press conference later Thursday morning.
She called basement fires "tricky" and emphasized the fact that smoke detectors can save lives. The building's owner said all units had working smoke detectors.
Chicago firefighters passed out fire safety materials in the neighborhood about 10 a.m.
"My mom all of a sudden comes into my room and she's like, 'Andale, andale, vente, vente!' And she's like 'get out of the house right now,'" said Sarah Blbuena, who escaped from the blaze.
She and her family got out in time, but those living under them were rushed to the hospital.
"I was just shocked because I've lived in that house so long and nothing has really happened," Blbuena said.
Richard Johnson has lived across the street from the building for 32 years.
"The flames coming up out of the basement window, going up 20-30 feet, it was just amazing," Johnson said.