Nine people in Ohio were killed "in less than one minute", according to Mayor Nan Whaley, after a shooter armed with an automatic rifle opened fire at a bar, marking the United States' second mass shooting in less than 24 hours.
Police say the 24-year-old white man behind the shooting, killed his sister and eight others before he was fatally shot by police.
The shooting unfolded at The Ned Peppers Bar in the arts and entertainment district of Oregon.
Authorities say Connor Betts was killed by police less than a minute after he started shooting a .223-caliber rifle into the streets of a popular Dayton nightlife area at 1am local time.
"In less than one minute, Dayton first responders neutralised the shooter," Mayor Whaley said.
They say his 22-year-old sister, Megan, was the youngest of the deceased victims, who were all killed in the same area. The others were adults ranging in age from 25 to 57.
They identified the other dead as Monica Brickhouse, 39; Nicholas Cumer, 25; Derrick Fudge, 57; Thomas McNichols, 25; Lois Oglesby, 27; Saeed Saleh, 38; Logan Turner, 30; and Beatrice N. Warren-Curtis, 36.
Twenty-seven people were injured, with medics reporting critical patients in the area of East 5th Street in the Oregon District. A total of 16 people were taken to Miami Valley Hospital, but their ages and the extent of their injuries remain unknown.
In a press conference, Mayor Whaley told reporters: "The gunman was wearing body armour and a had a 223 calibre high capacity magazines and extra magazines.
"27 have been injured, there were 10 fatalities in our community including the shooter."
Six of the nine killed were black, police said. Although they'll investigate the possibility of a hate crime, they said the quick timing of the violence made any discrimination in the shooting seem unlikely.
Mayor Whaley praised Dayton police, saying: "If she hadn't got to the shooter within a minute, hundreds could be dead now. The quickness of Dayton police saved literally hundreds of lives."
Witnesses said they saw a man dressed in black open fire with an automatic rifle, hitting up to 20 people. One witness said he heard "40 or 50" shots being fired.
Daniel Williams, a former member of the rock band The Devil Wears Prada, said he was in the bar at the time of the shooting.
"I am so incredibly heartbroken for those affected by this. I have never been so scared in my life," he told BNO News.
Speaking to the BBC, Jae Williams said he was at a nearby rap performance when they were told to evacuate.
"I was very shocked," he said. "We all evacuated quickly and safely. We were told to avoid the Oregon district.
"I got to my car, I could see cops, multiple ambulances. When I drove past I saw a lot of cops and ambulances."
Taylor Mayberry, who said she was inside the Ned Peppers bar when the shooting took place, told NBC News she hid in the bathroom as "tons of gunshots" were firing.
"I just heard a few gunshots and then saw everyone jumping to the ground," she said. "I've never experienced anything like that, so I dove to the ground and started running to the bathroom. I saw people trying to move toward the exit."
She said she was one of the last people to be let into the bathroom, where 10 others were already hiding. "We were holding the door shut and waiting until the gunshots stopped," Mayberry said.
"People were banging on the doors throughout. We weren't sure if they were…you know…we weren't sure if it was people getting in to shoot us or to get safe."
"All of our staff is safe and our hearts go out to everyone involved as we gather information," the bar said in a post on Instagram.
Dayton local and eyewitness James Williams said the incident took place at a bar called Ned Peppers, while he was seated in front of the patio.
In a video posted to Facebook, Williams said the active shooter had an AR-15. "He came up with an AR-15, had a vest on, earmuffs, and just started blowing bullets everywhere. I'm safe, there are casualties everywhere... they've taken ambulances of people everywhere. It's awful. I've never seen anything like this before."
Dayton's deputy police chief Matt Carper said the suspected shooter appeared to have fired with a long gun.
"Fortunately we had multiple officers in the immediate vicinity when this incident started," he told reporters. "For that we are very fortunate."
He added: "This is a very tragic incident and we are doing everything we can, to investigate it and try to identify the motivation behind this."
Investigators are still working to determine the killer's motive. Police have asked local residents to avoid the area.
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," 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 dumpster.
"It was so noisy, but then you could tell it was gunshots and there was a lot of rounds," Leonard said.
Meanwhile, Ohio Governor Miek DeWine has ordered flags in the state to be lowered "in honour and memory of the victims who lost their lives".
"Fran and I are absolutely heartbroken over the horrible attack that occurred this morning in Dayton. We join those across Ohio and this country in offering our prayers to victims and their families," the governor said. "I commend Dayton Police and other first responders for their bravery and quick response to save lives and bring an end to this tragedy."
The Ohio shooting came hours after a young man opened fire in a crowded El Paso, Texas, shopping area, leaving 20 dead and more than two dozen injured. Just days before, on July 28, 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 is the 22nd mass killing of 2019 in the US, according to the AP/USA Today/Northeastern University mass murder database that tracks homicides where four or more people were killed — not including the offender. The 20 mass killings in the US in 2019 that preceded this weekend claimed 96 lives.
Some of the deadliest mass shootings in the US in the last two years:
• August 4, 2019: A gunman wearing body armour shot and killed nine people at a popular nightlife area in Dayton, Ohio. Police were patrolling the area and killed the suspect.
• August 3, 2019: A gunman opened fire at a shopping center in El Paso, Texas, killing 20 people and injuring more than two dozen. A suspect was taken into custody.
• May 31, 2019: Longtime city worker DeWayne Craddock opened fire in a building that houses Virginia Beach government offices. He killed 12 people and wounded several others before he was gunned down by police.
• February 15, 2019: Gary Martin killed five co-workers at a manufacturing plant in Aurora, Illinois, during a disciplinary meeting where he was fired. He wounded one other employee and five of the first police officers to arrive at the suburban Chicago plant before he was killed during a shootout police.
• Noember 7, 2018: Ian David Long killed 12 people at a country music bar in Thousand Oaks, California, before taking his own life. Long was a Marine combat veteran of the war in Afghanistan.
• October 27, 2018: Robert Bowers is accused of opening fire at Tree of Life synagogue in Pittsburgh, Pennsylvania, during Shabbat morning services, killing 11 and injuring others. It's the deadliest attack on Jews in the U.S. in history.
• June 28, 2018: Jarrod Ramos shot through the windows of the Capital Gazette offices in Annapolis, Maryland, before turning the weapon on employees there, killing five at The Capital newspaper. Authorities say Ramos had sent threatening letters to the newspaper prior to the attack.
• May 18, 2018: Dimitrios Pagourtzis began shooting during an art class at Santa Fe High School in Santa Fe, Texas. The 17-year-old killed eight students and two teachers and 13 others were wounded. Explosive were found at the school and off campus.
• February 14, 2018: Nikolas Cruz shot and killed 17 students and staff members at Marjory Stoneman Douglas High School in Parkland, Florida. It surpassed Columbine High School as the deadliest shooting at a high school in U.S. history.
• November 5, 2017: Devin Patrick Kelley, who had been discharged from the Air Force after a conviction for domestic violence, used an AR-style firearm to shoot up a congregation at a small church in Sutherland Springs, Texas, killing more than two dozen.
• October 1, 2017: Stephen Paddock opened fire on an outdoor music festival on the Las Vegas Strip from the 32nd floor of a hotel-casino, killing 58 people and wounding more than 500. SWAT teams with explosives then stormed his room and found he had killed himself.
- with AP