"The specialness of the day doesn't appear to interrupt the relentless drumbeat of violence," Mayor Mitch Landrieu said at a news conference outside a hospital where victims were being treated Sunday night.
Mary Beth Romig, a spokeswoman for the FBI in New Orleans, characterized the shooting as street violence.
As many as 400 people came out for the second-line procession — a boisterous New Orleans tradition — though only half that many were in the immediate vicinity of the shooting, Police Superintendent Ronal Serpas said. Officers were interspersed with the marchers, which is routine for such events.
Second-line parades are loose processions in which people dance down the street, often following behind a brass band. They can be planned events or impromptu offshoots of other celebrations. They trace their origins to the city's famous jazz funerals.
Police saw three suspects running from the scene. No arrests had been made as of late Sunday.
Outside the hospital Sunday night, Leonard Temple became teary as he talked about a friend who was in surgery after being shot three times during the parade. Temple was told the man was hit while trying to push his own daughter out of the way.
"People were just hanging out. We were just chilling. And this happened. Bad things always happen to good people," said Temple, who was at the parade but didn't see the shootings.
A social club called The Original Big 7 organized Sunday's event. The group was founded in 1996 at the Saint Bernard housing projects, according to its MySpace page.
The neighborhood where the shooting happened is a mix of low-income and middle-class row houses, some boarded up. As of last year, the 7th Ward's population was about 60 percent of its pre-Hurricane Katrina level.