The trains collided just before 8 a.m. when one train hit another train stopped at the Harlem station on the same track, according to Fox Chicago.
Forest Park Mayor Anthony Calderone said 48 people were taken to 10 area hospitals after the crash, according to NBC Chicago.
The Chicago Sun-Times reports the CTA initially said at least 11 people were injured in the crash.
CTA officials previously told the Chicago Tribune none of the injuries were life-threatening, according to the agency.
This shot was posted to Instagram shortly after the collision: