Gunmen opened fire on dozens of people marching in a Mother's Day neighbourhood parade in New Orleans on Sunday, wounding at least 19, including two children.

Police said that many of the victims were grazed and most of the wounds weren't life-threatening. No deaths were reported.

FBI spokeswoman Mary Beth Romig said federal investigators have no indication that the shooting was an act of terrorism.

"It's strictly an act of street violence in New Orleans," she said. The southern city has one of the highest violent crime rates in the US.

A news release said the wounded included two 10-year-olds. It also said two people were in surgery.

As many as 400 people joined in the procession that stretched for about 3 blocks in what's known as a second-line parade, a loose procession in which people dance down the street, often following behind a brass band. They can be impromptu or planned and are sometimes described as moving block parties.

Officers were interspersed with the marchers, which is routine for such events. Only about half the participants were in the immediate vicinity of the shooting, Serpas said.

Police saw three suspects running from the scene. No arrests had been made as of late afternoon.

A social club called The Original Big 7 organised Sunday's event. The group was founded in 1996 at a housing project, according to its MySpace page.

The neighbourhood where the shooting happened was a mix of low-income and middle-class houses, some boarded up. As of last year, the neighbourhood's population was about 60% of its level before Hurricane Katrina devastated New Orleans in 2005.

Police vowed to make swift arrests.

"We'll get them. We have good resources in this neighbourhood," Serpas said.