Service has been temporarily suspended between the Fullerton and Sox/35th stations. As a result of the disruption, trains were running from Howard and Fullerton and between 35th and 95th.
The CTA advised riders to use alternatives such as nearby bus routes and other rail lines.
"We are working to restore service as quickly as possible. Allow extra travel time," the CTA said.
The disruption is a result of a stalled train near Roosevelt, the CTA said. Shortly before 8:30 a.m., the CTA said trains were moving again with residual delays.