A traffic accident early this morning that injured two people may have been caused by an exchange of gunfire between the vehicles on the Dan Ryan Expressway, police say.

The incident began around 1:15 a.m. while the vehicles were traveling southbound on the Dan Ryan at 31st Street, according to the Illinois State Police.

Investigators suspect someone in one of the cars may have fired at occupants of the second vehicle.

The crash occurred on the expressway near 63rd Street.

One person with a fractured hip was taken to Advocate Christ Hospital in Oak Lawn. Another female was transported to St. Bernard Hospital where she was treated for a gunshot wound to the hand. She was later released and sent to the Chicago Police 2nd District station at W. 51st Street and S.Wentworth Avenue for questioning, as were two others involved in the incident.

Troopers found shell casings and a Ruger 9mm at the scene, but do not know the circumstances under which the shots were fired, says Illinois State Police Master Sgt. Todd Borisy.

No charges have been filed in connection with the incident, police say.