Chief Fred Fletcher said Officer Sean Lynch, 38 was taken to Erlanger. He is suffering from "serious" injuries but is expected to be okay.
A CST Hotel Transport van was also involved in the crash. The driver is Gary Evans, 55. He was taken to the hospital with minor injuries.
A third car was involved in the crash, driven by Marlene Williams.
Williams said she saw the police officer driving down Dodson Avenue toward the intersection with his sirens and lights flashing. Police say Officer Lynch was on his way to assist another officer.
"And when he got ready to make that turn that truck come from nowhere, that van, I don't know if he thought he was going to try and beat the police car or what. Ran right in to him," she said, "When he hit that car it just kept on sliding and it slid into our car."
The impact crushed the driver's side of the patrol car. Witnesses rushed to try and help the officer.
"Some guys over here at the service station came and tried to open the door to get him out but they couldn't," she said.
Williams and her seven-year-old granddaughter were shaken up but unharmed.
Chattanooga police are still investigating what caused the crash. Charges are pending.