The Morton Grove Police Department said the partial floor collapse happened at a condominium complex in the 5900-block of Lincoln Avenue.
ABC7 crews could not see the extent of the damage, but the collapse appears to have happened in the middle of the building.
Police helped the Morton Grove Fire Department evacuate the four-story building, which has more than 30 units, and no injuries have been reported.
At one point, people were standing on their balconies, waiting to be rescued.
ABC7 talked to residents about the chaos they experienced, with some describing a loud bang they heard as the floor caved in.
Some windows were blown out as the collapse happened. One resident said his car, parked in the basement, was destroyed.
At least 50 people were reportedly displaced by the collapse, and the American Red Cross is working to help them find temporary housing.
Nine different fire departments responded to the scene. The block is closed to traffic, and police asked the public to avoid the area.
What caused the collapse was not immediately clear.
Authorities did not immediately provide further information.
This is a developing story. Check back with ABC7 for updates.