At about 7:30 p.m., two people were shot, including a young person, police said. They were hospitalized, but police did not disclose their conditions.
Police were looking for a person of interest who was wearing a black sweatshirt and captured on store surveillance.
Worker Darrell Grigsby was outside when gunfire rang out.
"Everybody hit the ground. That's when a lady said that a little boy got shot. It was like a war. They were shooting at each other," Grigsby said.
The shooting started with an argument in the parking lot and several people ran into the store, causing panic. People hid in aisles and in a back warehouse until police gave an all-clear.
The Walmart Supercenter is located along the busy commercial district along U.S. Route 30.
The parking lot was blocked off late Sunday with multiple emergency vehicles in the area.