|Photo from Google Streetview|
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Update: A reader sent in the photo below at 8:25 and says: "The police/firefighters seem to be going into the sewer behind that building."
Update: A commenter says, "A news cameraman told me that a water main broke and the basement was flooding. They had to turn off the heat and electricity to fix it and were preparing to carry all the tenants out by hand (phew!). They were able to fix the problem before that became necessary, although at this point there are still a few fire trucks out front."
Update: According to this story on NBC Chicago, it was a broken water main that flooded the basement of the high-rise with five feet of water.