The attack was reported at around 8:30 p.m. at the Walmart in Beavercreek, a town of about 50,000 in the Dayton metropolitan area, AP reported.
“The conditions of the victims right now is unknown" but all were taken to hospitals for treatment, police Capt. Scott Molnar said at a news conference.
Police also said the gunman died after apparently shooting himself. His name, a motive for the attack and other details weren't immediately released.
Police earlier said on social media that the store had been cleared and secured and there wasn't any “active threat.”
“We’re heartbroken by what’s happened at our Beavercreek, Ohio store. This remains a developing situation, and we’re working closely with investigators on the scene,” Walmart said in a statement.