DAYTON (Ohio) — An assailant armed with a rifle opened fire in a downtown district of Dayton, Ohio, early on Sunday (Aug 4), killing nine people and wounding at least 16 others in the second deadly mass shooting in the United States in less than a day.

Police said they intervened to end the violence, leaving the shooter dead.

Assistant Police Chief Matt Carper said the incident began at 1am local time in Dayton's Oregon District, a downtown historic neighborhood known for its nightclubs, bars, art galleries and shops.

The motive behind the shooting was not immediately clear and that investigators believed the individual had acted alone, Mr Carper said.

Officers who were on patrol in the area reached the scene shortly after the shooting began to confront the shooter, whose identity, age or gender were not immediately disclosed.

"We had officers in the immediate vicinity when this shooting began and were able to respond and to put an end to it quickly," the Dayton Police Department said in a Twitter post.

A total of 10 people were killed, including the assailant. Sixteen others were taken to nearby hospitals for treatment.

FBI agents were assisting in the investigation.

The Dayton Daily News said the shooting occurred at or near an establishment called Ned Peppers Bar.

The newspaper cited a Facebook post from a person identifying himself as someone who was at the bar at the time who said the shooting happened in front of a patio area just outside the establishment.

Video footage posted on social media showed numerous police and fire department vehicles parked in the area.

The shooting in Dayton, a riverfront city of about 140,000 people in southwestern Ohio, followed the mass shooting at a Walmart store in El Paso, Texas, where 20 were killed and 26 others wounded on Saturday morning. REUTERS