Excerpts from abc7chicago.com:

The Chicago Fire Department responded to an extra-alarm fire near 119th Street and Avenue O in the Hegewisch neighborhood about 8:40 p.m. Wednesday. Flames and smoke could be seen from several blocks. The building was in an industrial area, and its roof appeared to be completely gone. There was a rekindle about 6:45 a.m. Thursday as more smoke could be seen coming from the demolished building.

From Chicago Fire Department Media on Twitter:

3-11 Alarm at 11909 S Avenue O. Staging area at 116th/Ave O. 2 sty ordinary 100×400 warehouse, fire

huge warehouse fire in Chicago

CFD Media photo

huge warehouse fire in Chicago

CFD Media photo

huge warehouse fire in Chicago

CFD Media photo