Sunday's deadly attack by a lone gunman in Las Vegas left at least 58 people dead and injured more than 500.

The attack on a country music concert taking place on the Las Vegas strip overtakes last year's mass shooting at a gay nightclub in Orlando as the nation's deadliest.

The Human Rights Campaign (HRC), the nation's largest LGBT rights advocate, responded in a statement.

“Our hearts are with Las Vegas and all those impacted by this horrific tragedy,” said HRC President Chad Griffin. “After Newtown, our nation called for action. After Tucson, Virginia Tech, Aurora, San Bernardino, Charleston, and Alexandria, we called for action. After the shooting at Pulse Nightclub a little more than a year ago, we called for action. Yet, in the face of these mounting tragedies, many of our lawmakers have refused to act on meaningful gun safety legislation. As these politicians fail to act, at least 58 people in Las Vegas were killed last night, while hundreds more have been injured. It’s time for Congress and the White House to act. We need leadership now, and we must continue to demand it until our lawmakers either hear us – or we have new lawmakers.”

LGBT celebrities also reacted to the news.

“It's unimaginable,” Ellen DeGeneres tweeted. “And yet it's real. I don't know where to begin. Watching, crying, and sending love.”

Melissa Etheridge messaged: “My heart beats with sadness today...sending love into the world is all I can do. This brings me to my knees...#LasVegasShooting #morelove.”

“God bless those killed or hurt in Las Vegas,” wrote Boy George. “I cannot bear it. It's just too upsetting.”

Olympian Gus Kenworthy added: “The saddest part is that this has happened before and that it will happen again. We NEED stricter gun reform.”