Footage of the off-duty agent dancing enthusiastically was captured by a bystander, in a video which has been shared thousands of times.
Dressed in casual trousers and a shirt, he springs backwards onto his hands.
As he lands, a gun falls out from his waistband onto the floor and goes off as he scrambles to quickly pick it up. He then tucks it into his waistband and raises his hands in the air as he walks away.
One of the other people in the club was hit in the leg by the bullet and taken to hospital. He was not badly hurt, according to Denver police.
In a statement, the Denver Police Department said the agent “was dancing at a nightclub when his firearm became dislodged from its waistband holster and fell onto the floor.
"When the agent retrieved his handgun an unintended discharge occurred.”
The incident is being investigated. The off-duty agent was interviewed by police before being released to a Federal Bureau of Investigation supervisor.
The Denver District Attorney’s office will decide whether to press any charges.
Denver district attorney spokesman Ken Lane declined to comment as the incident remains under investigation by police.
FBI spokeswoman Amy Sanders also said police were leading the investigation, and that it was a ‘personnel matter for the FBI”.
Reuters contributed to this report.
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