The fire broke out about 5:30 a.m. in the 7600-block of South Paulina Street in a two-story apartment building and quickly spread to another building.
The firefighter suffered minor smoke inhalation and was taken to Little Company of Mary Hospital, where he is listed in good condition, Chicago fire officials said.
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No tenants were hurt, but two people were displaced.
It was not immediately clear how the fire started, and its cause is under investigation.