The fire broke out in a two-story home in the 8400-block of South Seeley Avenue in Gresham just after 4 a.m., Chicago police said.
One person was taken to Christ Hospital in critical condition.
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Chicago fire officials said later Friday morning the person remained in critical condition.
Officials did not immediately provide any information on the victim's age or gender, and it was not clear how the fire began.
This is a developing story; check back with ABC7 Chicago for updates.