Jason Aldean, Jake Owen and Chris Young are among the artists who sent messages on Twitter and Instagram after a gunman opened fire on the crowd at the Route 91 festival in Las Vegas on Sunday night. Aldean, who was onstage when the shooting started, wrote an anguished message on Instagram, while Owen, who’d performed before him, posted a series of tweets as the shooting took place, including one sending love to his baby daughter, Pearl.

“Gun shots were ringing off of the stage rigging and road cases,” Owen tweeted. “No one knew where to go..thank you LVPD and responders for keeping us safe.”

“Spent I don’t know how long on the floor of a trailer behind the stage…know multiple people are dead. Listening to that gunfire,” Young tweeted. “I’m not gonna say anything else other than I’m lucky to be alive. As are many others… and so many people are gone… this is heartbreaking.”

More than 50 people were killed and 400 injured in the attack, the worst mass shooting in U.S. history. The suspected gunman, Stephen Paddock, 64, killed himself, police said.

“Tonight has been beyond horrific,” Aldean wrote. “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.”