Five people have been killed and 18 injured in a shooting at a gay nightclub on Saturday night in Colorado Springs, police said.
A suspect is in custody and being treated for injuries after the attack at Club Q, Colorado Springs Lieutenant Pamela Castro told a news conference.
Images of the scene after the shooting showed security and emergency vehicles with flashing lights parked on a street near the venue.
Police got the initial phone call just before midnight about the shooting, Ms Castro said.
In its Google listing, Club Q describes itself as an "adult-oriented gay and lesbian nightclub hosting theme nights such as karaoke, drag shows & DJs".
In a statement about the shooting posted to its Facebook page, Club Q said: “Club Q is devastated by the senseless attack on our community.
“Our prays and thoughts are with all the victims and their families and friends.”
The statement added: “We thank the quick reactions of heroic customers that subdued the gunman and ended this hate attack.”
Police said they received “numerous” 911 calls, beginning at around 11.57pm local time, and rushed to the scene, Ms Castro said.
“They did locate one individual who we believe to be the suspect inside,” she added. “At this point in time, the suspect is being treated, but is in custody.”
By 4am, police had taped off the area around the club, which is located in a strip mall on the outskirts of Colorado Springs.
Detectives have so far declined to comment on a potential motive for the shooting, although police confirmed that the FBI was assisting them with the investigation.
Mike Smaldino, Colorado Springs fire captain, said 11 ambulances responded to the scene after multiple 911 calls were received.
“We will be here for many, many hours to come,” Ms Castro said.
In 2016, a gunman killed 49 people at gay nightclub in Orlando, Florida, before he was shot dead by police. At the time it was the worst mass shooting in recent U.S. history.
The shooter had claimed allegiance to a leader of Islamic State. He was killed in an exchange of gunfire with police.