CFD said on X just after 9:15 a.m. that the collapse happened in the 6000-block of South Loomis Boulevard in Englewood.
Fire officials said no one was injured, and the building was vacant.
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Chopper 7 was over the scene about 9 a.m.
The back half of what appeared to be a residential building had collapsed, leaving a gaping hole.
It was not immediately clear what led up to the collapse.
This is a developing story; check back with ABC7 Chicago for updates.