A man shot and killed at least five people and injured 18 late on Saturday after opening fire at a Colorado nightclub, in the latest mass shooting in the US.
Police received first reports of the shooting at Club Q in Colorado Springs just before midnight on Saturday.
A man was in custody, police said, and had been treated for injuries.
“Heroic customers” overpowered the gunman during the “senseless” attack, the nightclub wrote on Facebook.
Police said “a 22-year-old gunman” immediately began firing from a “long rifle”.
Police Chief Adrian Vasquez confirmed that two patrons confronted the gunman and stopped the shooting.
“We owe them a great debt of thanks,” said Mr Vasquez.
The attack is the sixth mass killing in the US this month and comes in a year when the nation was shaken by the deaths of 21 in a school shooting in Uvalde, Texas.
Condolences came flooding in as Americans woke up to the news on Sunday morning.
US President Joe Biden mourned for "yet another community ... torn apart by gun violence" and reiterated his calls to address America's gun violence epidemic as a public health crisis.
"Places that are supposed to be safe spaces of acceptance and celebration should never be turned into places of terror and violence," Mr Biden said.
"When will we decide we’ve had enough?"
Among others to react was actress Mia Farrow, who expressed “so much love and heartbreak”.
The motive behind the shooting was not immediately known. There have been increased warnings from the federal government about right-wing domestic terrorism.
Just last week, Senator Gary Peters, chairman of the Senate Homeland Security and Governmental Affairs Committee, released a new report that indicated Washington was “not adequately addressing the rise” in white supremacist, anti-government domestic terrorism.
Many, including American anti-gun activist and founder of the “Moms Demand Action Group” Shannon Watts, pointed to increased extremist hate in the US, which has fuelled a slew of mass shootings in recent years.
They include the shooting at a Pittsburgh synagogue in 2019, a shooting at an El Paso Walmart in the same year that targeted Mexicans, and the shooting of Black Americans in Buffalo in May by an assailant who was radicalised online.
“What do these shooting attacks have in common? Extremists' hateful rhetoric and easy access to guns,” Ms Watts tweeted.
Democratic Congressman Adam Schiff echoed those sentiments on Sunday morning, warning that “attacks like these will only become more common if we don’t fight back”.
Far-right, pro-gun Colorado Representative Lauren Boebert called for an end to “lawless violence” and expressed condolences for the Club Q victims and their families.
This was not the western state of Colorado's first mass shooting to make national headlines.
The state endured the 1999 Columbine High School shooting, and in 2012, a gunman killed 12 at a cinema in Aurora during a midnight screening of The Dark Knight Rises.
The perpetrator, James Holmes, was sentenced to life without parole in 2015.
A gay nightclub in Florida was the target of one of the country's most deadly attacks in 2016.
Forty-nine people were killed and 53 injured when a gunman opened fire on patrons at the Pulse nightclub in Orlando.
The Associated Press contributed to this report