Atleastfive people have beenkilledand 18 injured after agunmanopened fire inside a gay club in the USstateof Colorado on Saturday night.
A suspect is in police custody and is being treated for injuries. Two "heroic" people in the club subdued the attacker, police say.
Club Q, in ColoradoSprings, wrote on Facebook that it was "devastated by the senseless attack" on its community.
US President Joe Biden said Americans "cannot and must not tolerate hate".
Police asked people to be patient while they worked to identifyvictimsand finalise the number of casualties, adding that some people had taken themselves to hospital.
Officers received an initial emergency call about an active shooter at 23:57 (06:57 GMT) on Saturday, they said.
The suspect was found inside the club. Two firearms were found at the scene, and the attacker is thought to have used a longrifle.
Police did not suggest amotivefor the shooting but said the investigation would consider whether it was a hate crime, and if more than one person was involved.
A firedepartmentspokesman said casualties had beentransportedto hospitals very quickly because of training for such events.
The FBI in nearby Denver said it was assisting local police with theincident.
Police chief Adrian Vasquez thanked the two club-goers who intervened to stop the shooter.
"Initial evidence and interviews indicate that the suspectenteredClub Q and immediately began shooting at people inside as he moved further into the club," he told a news conference on Sunday.
"While the suspect was inside of the club, at least two heroic people inside the clubconfrontedand fought with the suspect and were able to stop the suspect from continuing to kill and harm others. We owe them a great debt of thanks."
Astatementon the Club Q Facebook page thanked "the quick reactions of heroic customers thatsubduedthe gunman and ended this hateattack".
The club washostinga dance party at the time, and hadplannedto hold aperformanceevent on Sunday evening tocelebrateTransgender Day of Remembrance.
Joshua Thurman, 34, was in the club at the time of theshooting.
At first hethoughtthe shots were part of the music, he told theColoradoSun, but he later ran to take shelter in the club dressing room.
"When I came out there werebodieson the floor,shatteredglass, broken cups, peoplecrying," he said.
"There was nothingkeepingthat man from coming in to kill us. Why did this have tohappen? Why? Why did people have to lose their lives?"
MrThurman, who lives near theclub, said it was an important part of the local gaycommunity. He believes he knows one person who waskilled.
Governorof ColoradoJaredPolis, who is gay, praised the "braveindividualswho blocked the gunman, likely saving lives in theprocess".
"Coloradostands with ourLGTBQCommunity and everyoneimpactedby this tragedy as wemourn," he wrote in a Facebook post.
In astatementfrom theWhiteHouse,PresidentBiden said: "Placesthat are supposed to be safe spaces of acceptance and celebration should never be turned into places of terror and violence. Yet it happens far too often. We must drive out theinequitiesthat contribute to violence againstLGBTQI+ people."
Onepersonwrote that the club had been "like a home" for her for manyyears, and she was "absolutelyshattered" by the news.
"[I]metso many great people, I literally met myhusbandthere, so it holds such a special place in my heart. Everyone was always so welcoming and kind through the years," shewrote.
"Club Q has been the heart of ourcommunityfor so long and I am devastated and angered that this happened."
In 2016, 49peoplewere killed and more than 50 injured in ashootingat the Pulse gay club inOrlando, Florida. At the time itwasthe deadliestmassshooting in US history.
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