Sister Of Ohio Shooter Among Victims In Nightclub Massacre

The 24-year-old man behind a mass shooting in Dayton, Ohio, killed his sister and eight others before he was fatally shot by officers, police say.

Connor Betts was killed by police less than a minute after he started shooting a .223-calibre rifle into the streets of a popular Dayton nightlife area around 1am local time on Sunday.

Police said Betts' 22-year-old sister Megan was the youngest of the dead victims, who were all killed in the same area.

The others were adults ranging in age from 25 to 57; it was the second mass shooting in the US in less than 24 hours.

Investigators haven't publicly discussed a possible motive.

Connor Betts was shot dead by police. Photo: Twitter.

Dayton Mayor Nan Whaley said Betts was wearing body armour and had additional high-capacity magazines.

Had police not responded so quickly, "hundreds of people in the Oregon District could be dead today," she said.

The Oregon District is a historic neighbourhood that is home to bars, restaurants and theatres.

Whaley said at least 27 people were treated for injuries and at least 15 of those have been released.

Several more remain in a serious or critical condition, local hospital officials told a news conference.

READ MORE: One Day. Two Mass Shootings. 30 Dead.

Connor and Megan Betts. Photo: Twitter/ New York Post.

Nikita Papillon, 23, was across the street when the shooting started and said she saw a girl she had talked to earlier lying outside Ned Peppers Bar.

"She had told me she liked my outfit and thought I was cute and I told her I liked her outfit and I thought she was cute," Papillon said.

"People my age, we don't think something like this is going to happen.

"And when it happens, words can't describe it."

U.S. President Donald Trump has been briefed on the shooting and praised law enforcement's speedy response in a tweet on Sunday morning.

Governor Mike DeWine issued his own statement before 7am, announcing he had ordered flags in Ohio to remain at half-mast.

Clothing cleared from the Ned Pepper bar after the shooting. Photo: CBS News.

A family assistance centre was set up at the Dayton Convention Centre, where people seeking information on victims arrived in a steady trickle throughout the morning.

The Ohio shooting came hours after a young man opened fire in a crowded shopping area in El Paso, Texas, leaving 20 dead and more than two dozen injured.

READ MORE: Everything We Know About The Texas Shooting Suspect

Just days before, a 19-year-old shot and killed three people, including two children, at the Gilroy Garlic Festival in northern California.

Sunday's shooting in Dayton was the 22nd mass killing in the U.S. this year.

The first 20 mass killings in the U.S. in 2019 claimed 96 lives.