Smoke led to the evacuation of the building.
"First of all, you know, we have fire drills all the time. It was on the 14th floor. So they got and said this is not a drill, this is an actual fire, everybody must vacate the building immediately. Everybody was very cool. We filed out. It was well done. Here we are standing on the street," said Elizabeth Bertucci, worker.
"Our main exit route, they had just had some construction done so that stairwell was walled off so a lot of people were nervous, didn't know where to go. We ended up going down a different set of stairs," said Issac Molmgren, worker.
Several people were treated at the scene, according to officials, but only one person was transferred to a local hospital. She is listed in good condition at Northwestern Memorial Hospital.
The small fire is believed to have begun in the 15th floor of the building. Officials are letting the high-rise air out before allowing people back in.
The Continental and Commercial National Bank Building is one of the last buildings designed by Chicago architect Daniel Burnham. It was built in 1914, two years after his death.
Floors 1-12 are under construction, but the top floors are occupied.