Chopper 6 was over the scene around 8 p.m. as officers responded to the Walmart along North MacDade Boulevard in Darby Township.
According to investigators, two men were arguing inside the store when one of them pulled out a gun and fired between five and 10 shots.
A female Walmart employee was struck in the calf. She was taken to a hospital with non-life-threatening injuries.
One woman working as a DoorDash driver said she was in a nearby store when people were told to get on the ground.
"The cops came over with their rifles and told everyone in the store to get down. I had no clue what happened," she said. "It's crazy. You can't even shop anymore. It's ridiculous."
The gunman fled the scene and remained at large Friday night.
"There is no reason to believe that there is any danger to the public at this time. Our thoughts are with those who have been affected by this senseless act of violence," the Delaware County District Attorney's Office said in a statement.
Police have not identified the wanted gunman.
Anyone with information is asked to contact Darby Township police.
Stay with Action News as we continue to follow this developing story.