Two of the wounded were in critical condition, Toledo Deputy Police Chief Joe Heffernan said. He said it appeared there were at least two people firing weapons who were "probably shooting at each other."
The Toledo Police Department said the shooting happened on Saturday afternoon near the Old West End Festival, an annual gathering of live music and home tours in a historic district of the city.
The department said an active search was under way for those responsible.
Multiple videos posted to social media showed people running over the sound of gunshots and emergency officials tending to others who appeared wounded.
Kevin Berry said he was sitting in the neighbourhood arboretum listening to live music with his friends when he heard a handful of gunshots ring out.
"Everybody hit the deck," he said.
When he looked back up, he saw a gun being tossed to the ground less than 15m away from him. Police officers who were already on-site for the festival immediately responded to the scene.
Berry, who has medical training and served in the US Navy, said he walked around the area looking for potential victims who might need help.
He said he saw at least five people with gunshot wounds.
"The folks who were hit were spread out around the arboretum area," he said.
The Old West End Festival is a two-day celebration in Toledo's historic district that includes live music, food vendors, home tours and shopping.
Berry described it as the "kick-off to Toledo's summer festival season."
Ohio Governor Mike DeWine said in a statement, sating "I am deeply concerned about the situation in Toledo tonight. Summer festivals should be safe spaces for families to spend time together without fear of violence,"
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