Streets around the Art Deco-style building, the corporate headquarters of LaSalle Bank in the city's downtown Loop business district, were closed to pedestrians and traffic as officials investigated the cause and tried to determine if the building was structurally sound.
More than 300 firefighters battled the blaze Monday night, shooting water into the windows and sometimes standing on the building's wedding cake-like tiers to gain better access. Office workers who escaped the blaze in the 43-story building said firefighters escorted them through blinding smoke to safety.
Of the 37 people injured, 22 were firefighters in moderate to serious condition, said fire commissioner Cortez Trotter. Most were being treated for smoke inhalation or minor injuries, officials said.
Investigators sealed off the 29th floor to preserve evidence and allow engineers to ensure it is structurally sound, Chicago Fire Department spokesman Larry Langford said.
Fire and police officials going above the first floor had to be decontaminated so they didn't track anything into the scene — a problem identified after a fatal Chicago high-rise fire 14 months ago that killed six people.
"We're going to do this very carefully and by the book," Langford said. "We're going through extreme measures."
CBS News Correspondent Cynthia Bowers reports torrential flames cascaded out windows as smoke filled the building, sending hundreds of workers scrambling for safety.
Many tried to escape down darkened stairwells, only to be turned back by smoke. Others waited for rescue wherever they could.
Bob Bailey, a partner in a commercial real estate law firm on the building's 39th floor, said he had to keep his head outside a window or near the ground because of the smoke until firefighters came and led him down an elevator.
"We had our windows open in the office and I had to put my coat on the door, so that smoke wouldn't start rolling in," he said. "And for a while, we weren't sure we were going to make it."
The fire at 135 S. LaSalle Street was reported about 6:30 p.m. and extinguished about midnight. Thick black smoke poured out of windows, and metal window frames were twisted by the heat of the blaze on the 29th and 30th floors.
More than one-third of the city's fire equipment was at the scene, and suburban fire departments sent crews into the city to act as backup.
Jim Rubens, who works at a law firm in the building, said he held hands with other victims as firefighters escorted them down a smoky stairwell.
"It was horribly thick smoke and the halls were completely dark," said Rubens, who was sweating and covered in black soot. "And we were trying to touch the person in front of you to see where we were going to."
The fire comes little more than a year after a 35-story county building in downtown Chicago caught fire, killing six people. A state-funded investigation concluded the deaths could have been prevented if there had been sprinklers and unlocked stairwells, and if firefighters had searched for victims sooner and kept out smoke and heat.
Several people who escaped Monday's fire said none of the stairwell doors were locked, fire alarm announcements told them clearly what to do and that firefighters found them and led them to safety.
But The Chicago Tribune reported that some employees who evacuated said an alarm sounded first, accompanied by a message telling them to remain calm and not evacuate. About 10 minutes later, witnesses said, a second alarm sounded and a message ordered everyone to evacuate.
LaSalle Bank spokesman Shawn Platt said the bank conducted a safety drill about a month ago, but there were no sprinklers on the 29th floor, which holds the bank's trust division. He said the building was putting in the infrastructure for sprinklers.
About 3,000 people work in the building. Most people there work normal business hours, but some departments are open 24 hours. The 29th floor, where the fire originated, is home to LaSalle Bank's trust division.
Lasalle Bank is one of the largest banks in the Midwest. Its building was originally named the Field Building, after Chicago retailer Marshall Field, whose estate developed the skyscraper in the early 1930s. It was designated a Chicago landmark in 1994.