Shots were fired in the car park of Club Blu in Fort Myers shortly after midnight, local time.
Eyewitnesses told of how they had to hide behind cars to dodge bullets, while others were shot as they tried to escape.
The club, which advertises itself as a “New Orleans style soulfood restaurant and lounge” was reportedly hosting a “swimsuit glow party” for teenagers.
The incident comes less than two months after Omar Mateen killed 49 people and wounded 53 others in gay nightclub Pulse, in Orlando, around 200 miles away from Fort Myers.
It is believed that three people have since been detained by police. Meanwhile, two other locations have been identified as connected with the shooting - a home, where the house and vehicles were shot at, according to police and another area where one of the suspects was arrested.
Mother Syreeta Gary told American TV channel Fox 4 that her daughter escaped the shooting, but said that the girl’s best friend was shot in the leg.
She said: “I just thank God that my daughter is OK, because she could have been shot. Her dodging bullets and running dropping between cars is what these kids have to go through, can’t enjoy themselves because these other people have criminalistic minds and want to terrorise things.”
Florida musician Nieya McGriff, who was performing at the event, said on her Facebook page that she was in the car park when the shots were fired.
“As soon as I’m on my way back to the car they started shooting,” she wrote.
She added while the incident was ongoing: “Bodies still on the ground y’all idk who at hospital.”
A statement from the Fort Myers Police Department said: “The Fort Myers Police Department and Lee County Sheriff’s Office are actively canvassing the area looking for other persons who may be involved in this incident. At this time the scene is still very active as investigators and crime scene personnel attempt to determine what occurred.”
It added: “The police department is attempting to determine a motive for this incident.”
Members of the public paid tribute to those killed and injured on social media.
Marissa Grear wrote: “Sending prayers and good vibes from Memphis. My heart is with everyone involved and their families. Praying for those recovering and those who have passed on.”