At least nine people have been shot dead outside a bar in Ohio, just hours after 20 people were killed in a shooting at a Walmart in Texas.
A police spokesperson said at least 16 people had been taken to hospital following the Ohio incident.
The suspected gunman is also dead.
According to a further police statement, the shooting began at 1am local time (6am in the UK) in the city’s Oregon District, which is home to a number of bars and restaurants.
It added: “We had officers in the immediate vicinity when this shooting began and were able to respond and put an end to it quickly.”
The FBI is also involved in the “large scene and investigation”.
Pictures of the scene captured by witnesses outside Ned Peppers Bar in the neighbourhood showed a police cordon surrounding the area.
One witness, James Williams, who said he was sitting outside the bar at the time of the incident, recalled a man carrying a rifle approaching the area before opening fire.
He said on Facebook: “The active shooter he tried to go into the bar but did not make it through the door someone took the gun from him and he got shot and is dead.
“A bunch of people was taken to hospital I don’t know how many this place is a disaster.”
In a further video to Facebook, Mr Williams added: “It’s awful. I’ve never seen anything like this.”
Twitter user Hannuh also said she was at the bar at the time of the incident, writing on the social media platform that she had been left “speechless and heartbroken”.
She said of the incident: “We heard gunshots while on the patio…We ran for our lives and hopped a fence trampling multiple people in the process/hid anywhere we could.
We heard gunshots while on the patio.. ran indoors only to be shoved back out because the shots were coming from inside the bar. We ran for our lives and hopped a fence trampling multiple people in the process/hid anywhere we could https://t.co/pm7Q00DfbR
— Hannuh (@HannahRayNinja) August 4, 2019
“I am speechless and heartbroken and bawling my eyes out. I never expected to be in such a situation and have no words. This is the most terrible thing I’ve ever felt.
“There are no f****** words for this feeling. It is absolutely disgusting. My heart is in pieces for anyone inside the bar who was worsely affected by this.”
Another witness, Dougie Doug, broadcast live video to Facebook of the scene.
He added: “I heard the s***… there were at least 40 or 50 shots.”
They just shot up ned peppers while I was in line…. police just killed dude 5 feet in front of me… I can’t go out in this city anymore 💯
— Bocock (@D_Bocock) August 4, 2019
That was a life changing experience for me in Ned Peppers
— Anthony Freeman (@AntBankS___) August 4, 2019
On Twitter, one person said he was “the next person to get my ID checked” in the line for Ned Peppers Bar, “when dude started shooting five feet from me”.
In an earlier tweet, he said: “Police just killed dude five feet in front of me… I can’t go out in this city anymore.”
Dayton Police Department advised people in a tweet to avoid the Oregon District area of the city as the investigation developed.
Ned Peppers Bar confirmed in an Instagram post that all of its staff were safe after the shooting.
The post read: “All of our staff is safe and our hearts go out to everyone involved as we gather information.”
There have been more than 200 mass shootings – with at least four people shot – in the United States so far this year.
The shooting in Dayton is the 22nd mass killing in the US this year, while the shooting in Texas is the eighth worst mass shooting in modern US history.