A gunman opened fire inside a gay club in the US state of Colorado on Saturday night, killing five people and injuring 18.
A suspect was in custody and being treated for injuries, police said.
Club Q, in Colorado Springs, released a statement on Facebook saying it was “devastated by the senseless attack on our community”, and thanking customers who “subdued” the gunman.
In 2016, 49 people were killed in a shooting at a gay club in Florida.
Colorado Springs police said they received an initial emergency call about an active shooter at 23:57 (06:57 GMT) on Saturday.
The suspect was found inside the club when police entered.
Police did not immediately suggest a motive for the shooting and said the number of dead and injured could change as the investigation continues.
A fire department spokesman said casualties had been transported to hospitals very quickly, due to training for events such as this.
FBI Denver said it was assisting police with the incident.
A statement on the Club Q Facebook page thanked “the quick reactions of heroic customers that subdued the gunman and ended this hate attack”.
The club was hosting a dance party at the time, and had planned to hold a performance event on Sunday evening to celebrate Transgender Day of Remembrance.
The club’s Facebook page has been inundated with comments and condolences from around the world after the attack.
One person wrote that the club had been “like a home” for her for many years, and she was “absolutely shattered” by the news.
“[I] met so many great people, I literally met my husband there, so it holds such a special place in my heart. Everyone was always so welcoming and kind through the years,” she wrote.
“I am so broken by this news,” another comment added.
“Club Q has been the heart of our community for so long and I am devastated and angered that this happened.”
The office of Colorado Springs mayor John Suthers called the event a tragedy, and said the mayor will speak at a police press conference on Sunday.
In 2016, 49 people were killed and more than 50 injured in a shooting at the Pulse gay club in Orlando, Florida. At the time it was the deadliest mass shooting in US history.
President Obama called the Florida attack “an act of terror and an act of hate”.