Two people were killed and as many as 17 – one just 12 years old – wounded when gunfire erupted at a teen swimsuit party at a southwest Florida nightclub early Monday, according to reports.

Five people were detained by police, but it’s unclear if any were believed to be a shooter. Neither the shooter’s identity nor motivation was clear. Authorities are not sure if one shooter or multiple shooters were involved. The attack apparently occurred at a teen event billed as a “Swimsuit Glow Party” at Club Blu in Fort Myers, local media reported.

The shooting is “definitely not terrorism,” police told Fox News’ Heather Nauert. The incident appears to have been gang-related, a law enforcement official told Fox News’ Matt Dean.

“We are deeply sorry for all involved,” Club Blu posted on Facebook on Monday morning. “We tried to give the teens WHAT WE THOUGHT WAS A SAFE PLACE TO HAVE A GOOD TIME. Ages 12-17. There was armed security as well as full security, inside and out.”

The area was deemed safe hours later, Fort Myers Police Capt. Jim Mulligan said in a statement. Three people remained hospitalized with serious injuries, local station WINK-TV reported. One of the victims was identified as Cherly Garn, 12, a spokeswoman for Lee Memorial Health System, told WINK.

The shooting came more than a month after a terror attack at a nightclub in Orlando that was the deadliest shooting in modern U.S. history. The shooting at the Pulse nightclub on June 12 left 49 dead and 53 others wounded.

The violence at Club Blu erupted about 12:30 a.m. Monday, and there were two active crime scenes, Mulligan said. Several hours later a street in the area remained closed as police investigated.

“As the club was closing and parents were picking their children up…..that’s when all this took place,” Club Blue posted on Facebook. “There was nothing more we could [have] done [as] you see it was not kids at the party that did this despicable act.”

The area was later deemed safe, but Mulligan said a street was still closed as authorities investigated.

In a statement, authorities said the Fort Myers police and the Lee County Sheriff’s Office were “actively canvassing the area looking for other persons who may be involved in this incident.”