Dozens of people were injured in Chicago when a crowded commuter bus traveled off a major thoroughfare and crashed into trees on Saturday.
Fire Department spokesman Larry Langford says around 70 people were on the Chicago Transit Authority bus when it veered off South Lake Shore Drive around 6 p.m. The impact caved in a front side of the bus.
Fire officials said 37 passengers were taken to the hospital, including four in critical condition.
Langford said more than 20 others were treated at the scene, mainly for bumps and bruises.
He said it's not known what caused the accident.
NBC station WMAQ and The Associated Press contributed to this report.