Thick smoke poured from the roof of a 45-story office building Wednesday, forcing workers into the downtown streets as firefighters rushed inside.

The fire was contained to equipment on the building's rooftop, and was not coming from inside, Fire Department spokesman Larry Langford said.

He said authorities were not ordering an evacuation, but were assisting people who wanted to leave. Emergency medical responders were checking some people as "a precaution," Langford said.

Rhonda Johnson, said she was on the 44th floor when co-workers noticed smoke on the outside of the west side of the building. They didn't know where the smoke was coming from, she said. "There was no noise."

Johnson said she took an elevator to the ground floor, where she saw firefighters rushing inside.

The building, just west of the Chicago River, has several commercial tenants, an Italian restaurant, a parking garage, and a child care center. The phone number listed to the child-care center reached a recorded message Wednesday afternoon. Several children had been led out of the building shortly after the smoke was reported.

The building is for sale, said Andrew Neilly of Gallen Neilly & Associates, a public relations company that works with the building's owner, Shorenstein Properties of San Francisco.