The shooting happened Monday evening at a Martin Luther King Jr. Day event.
CNN  — 

One person was killed and seven others were shot at a block party packed with more than 1,000 people celebrating Martin Luther King Jr. Day in Fort Pierce, Florida, Monday, police said.

All eight of those shot were adults and they were ferried to the hospital for treatment, St. Lucie County Sheriff’s Office Chief Deputy Brian Hester said at a news conference.

The person who was killed died Tuesday morning, Sheriff Ken Mascara said at a briefing.

“She’s a 30-year-old Fort Pierce native who was at the party with her six-year-old daughter,” Mascara said.

At least four others were injured as people ran for safety, the sheriff’s office said. One of those injured was a juvenile who was hurt as people rushed to flee the park where the event was being held, Hester said.

“As the shots rang out, people were just running in all directions,” Hester said. “There were people laying behind cars, laying behind anything they could lay behind. It was kind of hard to tell who was a victim and who was just hiding at that point.”

The shooting began at around 5:20 p.m. in Ilous Ellis Park, he said, where the community had gathered for an afternoon car show, dance performances, live DJ and kids activities to celebrate Martin Luther King Jr. Day, an event flyer shows.

In a video taken by a witness, attendees are seen dancing by their cars and enjoying the music when what sounds like gunfire begins to resonate over the song. People in the crowd start to rush away from the noise, some ducking behind cars or grabbing children’s hands and running across the street.

The incident marks the 30th mass shooting in the country this year, according to the Gun Violence Archive. Like CNN, the non-profit defines a mass shooting as one in which four or more people are shot, not including the shooter. So far this year, the US is averaging about two mass shootings per day.

Two sheriff’s deputies who were stationed in the park ran toward the scene and provided aid to those injured, Hester said. Several witnesses also helped to render aid and drive people to the hospital, he added.

The sheriff’s office has not named any suspects in the shooting, but investigators were following up on several leads from witnesses and community members Monday night.

Mascara said Tuesday the case has turned into a murder investigation

“There were over 50 shell casings that were recovered from the scene from three different calibers of weapons,” said Hester.

Investigators preliminarily believe the gunfire involved multiple shooters and resulted from “a disagreement of some sort between two parties,” Hester said.

“So many innocent people that were injured or hurt were not part of the disagreement,” he added.

“It’s really unfortunate and it’s sad that during a celebration of someone who represented peace and equality, a disagreement results in a use of guns and violence,” Hester said.

He estimated as many as 40 sheriff’s office personnel were working the case Monday night as they processed the scene, spoke to victims at the hospital and followed up on leads.

Investigators are asking anyone with information about the shooting to contact authorities or submit anonymous tips through CrimeStoppers. The sheriff’s department is handling the case because the Ilous Ellis Park is a St. Lucie County park.

Fort Pierce is a coastal city about an hour’s drive north of West Palm Beach.

CNN’s Amanda Jackson contributed to this report.