At least five people were killed and 18 wounded in a mass shooting at an LGBTQ nightclub in the US city of Colorado Springs, police said on Sunday.

Partygoers who were apparently marking the Transgender Day of Remembrance subdued the gunman, according to a Facebook post by the venue, Club Q, and police said they have the suspect in custody.

The shooting is the latest in a long history of attacks on LGBTQ venues in the United States, the deadliest of which took place at a nightclub in Orlando, Florida, in 2016.

"It's with a heavy heart I have to tell you that we had a shooting at a local club this evening," said Colorado Springs Police Department spokesperson Pamela Castro.

"We have 18 injured and five deceased. That number is subject to change as the investigation continues," she said. "The FBI is already on the scene and assisting."

Castro said police in the Colorado city received an emergency call just before midnight on Saturday (0657 GMT Sunday) saying that there was an active shooting at Club Q.

She said medical teams and officers responded and "they did locate one individual who we believe to be the suspect inside," adding that the suspect was in custody and being treated at a local hospital.

Club Q responded by saying it "is devastated by the senseless attack on our community."

"We thank the quick reactions of heroic customers that subdued the gunman and ended this hate attack," it posted on Facebook on Sunday.

Messages of support were pouring in by the hundreds beneath the post, some from as far away as Sweden, Britain, New Zealand, Germany and Australia.

The club had posted earlier on Saturday about an LGBTQ event starting at 8:00 pm.

"We're celebrating Transgender Day of Remembrance with a variety of gender identities and performance styles," the post read.

The Transgender Day of Remembrance is held annually on November 20 to honour the memory of trans people who were killed in acts of transphobic violence.

An emergency medical team including 34 firefighters and 11 ambulances was dispatched to the scene of the shooting, according to Colorado Springs Fire Department spokesperson Mike Smaldino.

"Unfortunately, these are events we do train for, as far as what we call a 'mass casualty,' so that is why we had such a big response," Smaldino said.

He added that some ambulances had to carry two or three victims to nearby hospitals.

The Colorado Springs Police Department said there would be an 8:00 am (1500 GMT) news conference on the shooting.

On June 12, 2016, a gunman opened fire inside the Pulse nightclub in Orlando, killing 49 people and wounding more than 50 in what was then the deadliest mass shooting in modern US history.

US President Joe Biden marked the fifth anniversary of the Orlando shooting last year, taking the rare step of saying he would designate the club as a national memorial.

Gun violence is a major problem in the United States, where more than 600 mass shootings have occurred so far in 2022, according to the Gun Violence Archive website.

The archive defines a mass shooting as a single incident in which at least four people are wounded or killed.

Mass shootings have repeatedly reignited debate on gun control, a hot-button issue in the country, though little headway has been made in Congress on calls for reform. (AFP)