At least nine people have been killed after a gunman opened fire outside a bar in Dayton, Ohio, in the early hours of Sunday morning, police have said.

It came less than 24 hours after another mass shooting in the US, when a lone gunman in El Paso, Texas, shot dead 20 people on Saturday.

Dayton police department said 10 people, including the gunman, had been killed, with another 16 people in local hospitals. The FBI is assisting with the investigation.

The city’s mayor, Nan Whaley, said the shooter was wearing body armour and used a “.223 high-capacity” gun during the assault.

“In less than one minute, Dayton first responders neutralized the shooter,” Ms Whaley said in a press conference.

Ohio shooting: Gunman kills nine after opening fire outside bar Show all 21 1 /21 Ohio shooting: Gunman kills nine after opening fire outside bar Ohio shooting: Gunman kills nine after opening fire outside bar Several officers (top left and right) firing at Connor Betts (bottom left), who they identified as the gunman, seconds after he began killing people outside a bar in Dayton, Ohio Dayton Police Department/EPA Ohio shooting: Gunman kills nine after opening fire outside bar Betts killed nine people including his sister, and injured 26 others. He was also shot dead at the scene by the responding officers Dayton Police Department/AP Ohio shooting: Gunman kills nine after opening fire outside bar The Anderson Manufacturing AM-15 rifle with a 100-round double drum magazine which Connor Betts used Dayton Police Department/EPA Ohio shooting: Gunman kills nine after opening fire outside bar Surveillance footage of people beginning to flee from the sound of gunshots fired by Connor Betts Dayton Police Department/EPA Ohio shooting: Gunman kills nine after opening fire outside bar Police officers move towards Connor Betts Dayton Police Department/EPA Ohio shooting: Gunman kills nine after opening fire outside bar The vehicle which Connor Betts traveled to the scene in Dayton Police Department/EPA Ohio shooting: Gunman kills nine after opening fire outside bar Bodies are removed from the scene of a mass shooting in Dayton AP Ohio shooting: Gunman kills nine after opening fire outside bar The city's mayor, Nan Whaley, said the shooter was wearing body armour and used a ".223 high-capacity" gun during the assault. “In less than one minute, Dayton first responders neutralized the shooter.” AP Ohio shooting: Gunman kills nine after opening fire outside bar The FBI is assisting with the investigation Derek Myers/AFP/Getty Ohio shooting: Gunman kills nine after opening fire outside bar It was the second mass shooting in the US in less than 24 hours AP Ohio shooting: Gunman kills nine after opening fire outside bar Witnesses comfort one another at the scene AP Ohio shooting: Gunman kills nine after opening fire outside bar Police tape drapes over a chair near a pile of shoes. The shooting took place in the popular bar and nightlife area, Oregon district Dayton Daily News via AP Ohio shooting: Gunman kills nine after opening fire outside bar Dayton police look for evidence Dayton Daily News via AP Ohio shooting: Gunman kills nine after opening fire outside bar Shoes piled outside the scene AP Ohio shooting: Gunman kills nine after opening fire outside bar Residents comfort each other as they await word on whether they know any of the victims AP Ohio shooting: Gunman kills nine after opening fire outside bar Authorities retrieve evidence markers AP Ohio shooting: Gunman kills nine after opening fire outside bar Evidence markers lay on the ground near a hotdog stand Reuters Ohio shooting: Gunman kills nine after opening fire outside bar Evidence markers rest on the ground after a mass shooting in Dayton, Ohio, U.S. August 4, 2019. REUTERS/Bryan Woolston BRYAN WOOLSTON Reuters Ohio shooting: Gunman kills nine after opening fire outside bar People fill the streets during a vigil EPA Ohio shooting: Gunman kills nine after opening fire outside bar Mourners gather to recognise the victims Getty Ohio shooting: Gunman kills nine after opening fire outside bar Mourners leave flowers and candles at the entrance of Ned Peppers bar Getty

On its Twitter account, the department said the active shooter situation began in the Oregon District at around 1am, but that officers “in the immediate vicinity” were able to “put an end to it quickly”.

Police believe there was only one shooter, and have not yet identified the suspect or a motive. Lieutenant colonel Matt Carper said the suspect used a long gun and fired multiple rounds.

Video from the scene near downtown Dayton showed a host of emergency vehicles on a street that had been cordoned off.

The Oregon District is a historic neighbourhood near downtown Dayton that’s home to entertainment options, including bars, restaurants and theatres. The shooting took place outside, on the 400 block of East 5th Street.

“This is extremely unusual, obviously, for any community, let alone Dayton,” Mr Carper said at a press conference. “In our Oregon District, this is unheard of.”

Miami Valley Hospital spokeswoman Terrea Little said 16 victims have been received at the hospital but could not confirm their conditions.

Kettering Health Network spokeswoman Elizabeth Long said multiple victims from a shooting had been brought to system hospitals but did not have details on how many.

“I’m heartbroken,” Ms Whaley tweeted early on Sunday, before thanking first responders for their efforts.

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Nikita Papillon, 23, was across the street at Newcom’s Tavern when the shooting started. She 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,” Ms Papillon said. She herself had been to Ned Peppers the night before, describing it as the kind of place “where you don’t have to worry about someone shooting up the place.”

“People my age, we don’t think something like this is going to happen,” she said. “And when it happens, words can’t describe it.”

Tianycia Leonard, 28, was in the back, smoking, at Newcom’s. She heard “loud thumps” that she initially thought was people pounding on a bin.

“It was so noisy, but then you could tell it was gunshots and there was a lot of rounds,” Ms Leonard said.

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

“Fran and I are absolutely heartbroken over the horrible attack that occurred this morning in Dayton, the statement said. “We join those across Ohio and this country in offering our prayers to victims and their families.”