Authorities in New Orleans are trying to determine what sparked a shootout between two groups of men that wounded 17 people in a crowded park.
The mayor called on witnesses to come forward, but no one has yet offered video of the shootout or descriptions or IDs of the gunmen, officer Frank Robertson said.
None of the injuries is believed to be life-threatening.
Hundreds of people were gathered on Sunday evening at Bunny Friend Playground - most for a block party and some for the filming of a music video - when two groups in the crowd opened fire on each other, police said.
Police were on their way to break up a big crowd when gunfire erupted at the park in the city's 9th Ward, police said in a statement.
Mayor Mitch Landrieu, speaking at a news conference aired on WWL-TV, called on people who were in the park to come forward with information. Police have also asked people with any video of the shooting to bring it in.
"At the end of the day, it's really hard to police against a bunch of guys who decide to pull out guns and settle their disputes with 300 people in between them. That's just not something you can tolerate in the city," Mr Landrieu said.
Ten people were taken to hospital in ambulances, and others went in private vehicles, police said.
Photos of the scene showed emergency workers wheeling some of the wounded on stretchers while other people who appeared to be in pain lay on the ground.
Police said 11 of the victims were under the age of 21. Most have been discharged from the hospital, but officials said one will likely never walk again.
Officers are still searching for the gunmen who opened fire in the park.