At least 58 people were killed – including two Canadians – and more than 500 people were injured at a music festival in Las Vegas on Sunday night.
The horrific incident has been described as the deadliest mass shooting in modern U.S. history.
A gunman positioned on the 32nd floor of the Mandalay Bay across the street from the Route 91 Harvest Festival opened fire just after 10 p.m. as country singer Jason Aldean performed.
Video posted online shows the moment Aldean stopped singing and ran off the stage.
Among the dead is Jessica Klymchuk of Alberta and Jordan McIldoon of B.C.
Police later identified the gunman as local resident Stephen Paddock, 64. They believe he shot himself as SWAT officers breached his hotel room door. Police said Paddock, who checked in to the hotel on Sept. 28, had at least 16 weapons in his room.
Concert-goers reported hearing what they described as automatic gun fire.
David Becker / Getty Images
Singer Jake Owen, who was offstage when the shooting started, told CNN it was “like shooting fish in the barrel.”
“It was raining off the top of the stage, you could hear it hitting trailers,” he recalled. “It was chaos. No one ever wants to ever be a part of anything like this ever again.”
Owen said the shooting went on for at least 10 minutes. "It was non-stop," he said.
On Instagram, Aldean wrote: “Tonight has been beyond horrific. I still don’t know what to say but wanted to let everyone know that Me and my Crew are safe.
“My Thoughts and prayers go out to everyone involved tonight. It hurts my heart that this would happen to anyone who was just coming out to enjoy what should have been a fun night.”
The three-day festival featured acts like Eric Church, Sam Hunt, Maren Morris and Canadian duo High Valley.
"Can't believe the news," read a tweet by High Valley. "In shock. Too close to home."
U.S. president Donald Trump tweeted Monday morning: "My warmest condolences and sympathies to the victims and families of the terrible Las Vegas shooting. God bless you!"
Artists from all different genres of music took to social media to share their shock and grief.
“Horrified to hear about the shooting in #LasVegas. My thoughts are with the victims and their families,” tweeted Mariah Carey. “Praying for everyone's safety.”
Brad Paisley tweeted: “Praying for everyone at #HarvestFestival. There are no words right now that suffice.”
“Love and prayers being sent to everyone in Vegas,” tweeted Darius Rucker.
Dan + Shay shared: “Feeling absolutely helpless watching the Vegas situation unfold via social media. Fans, friends, artists, crews, everybody, please be safe. This is so scary.”
MORE: Stars Share Shock, Grief In Wake Of Mass Shooting
Charles Kelley of Lady Antebellum tweeted: “My heart is sick over the news in Las Vegas. Praying 4 everyone in the country community & everyone at the scene.”
“Praying for everyone at Route 91,” wrote Lauren Alaina. “That crowd was one of the best I've played for all year. This news is devastating. My camp is home & safe.”
Sunday night's shooting was the second mass killing at a concert this year. In May, more than 20 people were killed in a bombing outside an Ariana Grande concert in Manchester, England.
In 2015, nearly 90 people were killed inside the Bataclan theatre in Paris when gunmen opened fire during am Eagles of Death Metal concert.
This article has been updated since it was first published.