Service was suspended after the Chicago Fire Department said it received a report of a derailed southbound Green Line train near 47th Street about 11 a.m. CFD said one car went off the rails but was still on the tracks and the rest of the cars appear to be stable.
WATCH: Firefighters evacuate riders from derailed Green Line
Thirty passengers were on the train in total. Seven of them were transported to area hospitals with minor injuries while the other 23 refused medical treatment, according to CFD District Chief John Giordano.
Jean Miller was one of those onboard the train when it derailed.
"It was, like, a little bumpy and then all of a sudden the one in front was, like, derailed," she said.
Drake Hills, another passenger, described seeing smoke minutes after the train left the 43rd Street station and noticing that the next car ahead was tilting significantly to the left.
"We've got a lot of individuals who are complaining about neck pain and a couple people who are grabbing their shoulders," Hills said.
Passenger describes evacuation of derailed CTA Green Line train
Riders on the train said they began to feel a rocking back-and-forth motion and then a jolt as the first car derailed.
"We saw that the car in front of us essentially got off the tracks and at that point, we saw that the car was completely tilted toward the left," Hills said.
Donald Bonds, the CTA's chief transit officer, said the cause of the derailment is not yet clear. Bonds also said there was some work being performed in the area, though it's not currently clear what type of work was being performed and whether it contributed to the derailment.
The Chicago Fire Department was seen taking people off the train and lowering them to the ground. By around 12:20 p.m., the last passengers were taken off the train and the truck used by CFD to evacuate the train pulled away.