CHICAGO (CBS)– An Oak Park police officer was shot while assisting with a traffic stop near the Eisenhower Expressway Thursday.

According to police, the officer was assisting the Forest Park Police with a traffic stop on Harlem Avenue near the expressway around 7 a.m. Police said the driver of the vehicle stopped by police, got out of the car and started shooting.

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CBS 2’s Steven Graves reports two people were shot. The gunman and officer are being treated at Loyola Medical Center. The suspect and the officer have serious injuries, but both are expected to be OK.

Oak Park police say this was a routine traffic stop turned into a shootout.

“No one knew what was going on,” said grocery store owner Sanjay Lal. “There’s some shooting that happened.”

“People were running away from the scene,” added Robert Clark. “Even people were running out of the CTA. Running, just moving.”

It started when Forest Park police pulled over a driver, but it’s unclear what for. Officers said the suspect got out of that car and started shooting.

Medics also took the suspect from the scene. But also caught in the middle of the shootout – a U.S. Postal Service truck. The worker was not injured.

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Investigators shut down the scene for five hours while they looked for evidence.

CBS 2 Chicago Staff