The St. Lucie County Sheriff’s Office said that the shooting unfolded at Ilous Ellis Park in Fort Pierce at around 5.20pm local time during an MLK Car Show and Family Fun Day, where more than 1,000 people were in attendance.
Gunfire broke out following what officials described as a “disagreement of some sort between two parties”.
“Multiple people were shot, it sounds like from our initial investigation here on scene there was a disagreement of some sort between two parties, and unfortunately, they chose to resolve that with guns,” St. Lucie County Chief Deputy Brian Hester said.
“It was mass chaos, as you can imagine, when shots rang out. There were a thousand plus people here at the event, and as the shots rang out, people were just running in all directions.”
Terrifying footage, obtained by WPBF-TV, captured people ducking, running and hiding behind cars as the gunshots rung out.
The video shows several children and families at the scene, including a woman running to safety while holding a baby.
Eight people suffered gunshot wounds, all of whom were adults. One victim remains in a critical condition while the conditions of the other seven is unclear.
Their identities have not been released.
It also remains unclear whether or not the two groups knew each other prior to the shooting and what the disagreement was over.
As well as the eight people shot, police said that four others including a child sustained non-life-threatening injuries during the ensuing confusion, reported the local station.
The sheriff´s office said that two deputies at the event responded immediately and aided victims.
“It’s really sad in a celebration of someone who represented peace and equality that a disagreement results in a use of guns and violence to solve that disagreement, and that´s what´s really sad to me about what happened here,” said Mr Hester.
“And then so many innocent people who were injured or hurt and were not part of the disagreement as well.”
AP contributed to this report