CHICAGO (CBS) — A woman in her 20s was wounded Sunday night in a shootout in the parking lot of a Jewel grocery store in Munster, Indiana.

A carnival at St. Thomas More Catholic Church had just ended around 10 p.m., when someone started shooting in the parking lot of the Jewel across the street. Police believe two groups of people were exchanging gunfire.

“There was one person in the parking lot that had heard the shots, attempted to run back for cover inside of Jewel, and appears to have suffered a graze wound to the back of her head,” Munster Police Lt. Ed Strbjak said.

Police said the woman was taken to the hospital. Her injuries were not considered life-threatening.

Several cars and a store window also were struck by bullets. Police said there were at least 20 shell casings in the parking lot.

Strbjak said police are talking to several witnesses and possible suspects as part of their investigation.