Emergency crews responded to Ontario Street and Fairbanks Court around 8:45 a.m. after a 57-year-old woman was struck by the bus.
CTA officials said the #3 King Dr. bus had just left the bus terminal and was making a left turn from Ontario to Fairbanks when it struck her.
Witnesses told police they saw the woman, who may have been on her cell phone, try to cross the street in the middle of the street when she was hit.
Passersby rendered what aid they could and tried to keep both the woman and the bus driver calm until help arrived.
"I gave her water, I gave her a hug because she was upset," witness Annie Hightower said. "Then I just wanted to make sure the driver was OK because they said she was devastated by what went on."
The woman remains hospitalized at Northwestern Memorial Hospital in serious but stable condition. She suffered severe injuries to at least one of her legs.
Update to Pedestrian struck by bus at Ontario & Fairbank: female patient was transported to Northwestern Hospital in SERIOUS but stable condition.— Chicago Fire Media (@CFDMedia) August 2, 2019
No one else was injured. The CTA is conducting its own investigation into the accident.