Terror in Las Vegas! Jason Aldean Onstage When Gunman Opens Fire

Late Sunday night, Las Vegas was the site of the deadliest mass shooting in U.S. history.

Over 50 people were killed while attending the final night of the Route 91 Harvest festival, which also left more than 400 injured. The gunman, who has been identified as Stephen Paddock, 64, used automatic weapons, firing from a 32nd-floor window at Mandalay Bay Resort and Casino.

Country star Jason Aldean was performing when shots rang out. He abruptly left the stage once he realized what was happening.

Aldean wrote on Instagram, "Tonight has been beyond horrific. I still dont 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. #heartbroken #stopthehate."

Jake Owen, who had performed prior to Aldean and witnessed the tragedy, told NBC, "I kind of just ran like everyone else. At one point, I was crouched down behind a cop car with about 20 other people that were people who had just come to the show.”

He added, "Everyone's asking if everyone's okay. There was blood on people. You can see a couple of folks in the street that looked like they had been shot, lying there. It was chaotic. It was literally like a movie that you feel like that you've seen before that's not real life… It was chaos for a pure seven to ten minutes.”

Paddock, a resident of Mesquite, Nevada, was found dead in his hotel room after officers used a controlled explosive device to gain entry. Police do not believe the incident was related to terrorism, but Paddock's motive is unknown. It has been revealed that his father Benjamin Hoskins Paddock was on the FBI Most Wanted list in the late 1960s.

"Extra" spoke with Jared Branch, who attended the festival with his girlfriend. They were able to escape and help get the injured to safety. He said, "We loaded probably 4 or 5 people that had been shot into the back of trucks and got them to the hospital."

He added about the horrifying scene, "Everybody was hysterical. There were people crying, they wanted to get in there to try and find their husbands."

After news of the mass shooting broke, many celebrities took to social media to express their sympathy, including Taylor Swift, Carrie Underwood and Luke Bryan.

Taylor tweeted, "There are no words to express the helplessness and sorrow my broken heart feels for the victims in Vegas and their families.”

See more celebrity reactions below.