The shooting outside a party for teenagers at a Florida nightclub where a 14-year-old and 18-year-old died and as many as 17 other people were wounded, was not an act of terror, police say.

The latest burst of gun violence to wrack the state took place just after 12.30am local time in the parking lot of Club Blu, where officers found "several victims suffering from gunshot wounds," the Fort Myers Police Department said in a statement.

Police identified the two dead as Stef'An Strawder, an 18-year-old basketball star at a local high school, and Sean Archilles, 14.

"Investigators are working very hard to determine a motive," police said.

"The Fort Myers Police Department would like to confirm that this incident is not an act of terror (as it has been referred) or terrorism."

Besides the two fatalities, a local hospital said there were 17 other victims, ranging between ages 12 and 27. Police put the number of wounded at 14 to 16, with their injuries ranging from minor to life-threatening.

Police said three people had been detained for questioning and that the area was deemed safe, although roads in the vicinity remained closed.

The shooting came six weeks after a massacre at a nightclub in the Florida city of Orlando, where a lone gunman who sympathised with Islamist extremist groups killed 49 people in the deadliest mass shooting in modern US history.

Club Blu, located about 240km southwest of Orlando in the Gulf Coast city of Fort Myers, was hosting a "swimsuit glow party" for people all ages, according to a flyer posted on Twitter by local television station WINK.

To enter, patrons were not required to show proof that they were the legal age to drink alcoholic beverages.

The nightclub said on its Facebook page that the shooting occurred when the venue was closing and parents were picking up their children.

"We tried to give the teens what we thought was a safe place to have a good time," the nightclub said, pointing out that armed security guards were posted inside and outside the club.

"It was not kids at the party that did this despicable act."

One of the victims died after being admitted to the Lee Memorial Hospital in Fort Myers while the second victim died at the scene of the shooting.

Police said shots were also fired at a nearby residence, where there was one minor injury.