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CHICAGO, Illinois (CNN) -- A northbound Chicago subway train derailed shortly after 5 p.m. Tuesday, forcing the evacuations of dozens of passengers, a transit official said.

Seventy-six commuters were taken to nearby hospitals for treatment.

Chicago Transit Authority President Frank Kruesi said there was also a fire, but he had no details of the derailment.

""It's still very smoky down there," he said.

Firefighters led commuters from the underground tunnel and out an emergency exit, where they were met by emergency services.

Emergency workers set up triage areas on the street to distribute oxygen and water to passengers needing it.

Dozens of soot-covered commuters climbed out an emergency exit, a spokeswoman for the CTA said.

Wanda Taylor said service was shut down between the Damen and Racine stations on the CTA's Blue Line, which connects downtown Chicago and O'Hare International Airport.

One passenger told CNN that the train car she was riding in filled with smoke with no warning.

Bus service between the two stations was being established, Taylor said.