Police Superintendent Ronal Serpas told CNN affiliate WVUE that it appears "two or three people just, for a reason unknown to us, started shooting at, towards, or in the crowd."
He asked anyone with information to call authorities.
New Orleans Mayor Mitch Landrieu echoed that request, challenging the community to get involved.
"It's important for us, as I have said, to change the culture of death on the streets of New Orleans to a culture of life, and it's going to take an all-hands-on-deck approach," he said.
"These kinds of incidents are not going to go unanswered. We're going to be very, very aggressive. There were hundreds of people out there today, so somebody knows who did this."