The shooting happened around 8:33 p.m. near 9th and Walnut streets.
Sources told Action News that a man shot a woman during the incident.
After police arrived on the scene, investigators said at least one officer fired a weapon, striking the suspect. He was taken to an area hospital in critical condition.
Chopper 6 over police-involved shooting in Chester, Pa.
There was no immediate word on the woman's condition.
Chopper 6 video showed more than two dozen evidence markers scattered throughout the scene. Officers were also seen inspecting a dark-colored SUV at the location.
Police said no officers were injured.
Further details about what led up to the officer-involved shooting have not been released.