"It's too preliminary to tell," Landrieu said, adding that he expected more information later.
"It's a culture of violence that has enveloped this city for a long period of time ... and it's one of the things that we as a community have got to stop," the mayor said.
The attack included shots that were fired from different guns, police said Sunday, and officers saw three possible gunmen running from the scene.
On Monday, at least three victims were in critical condition, said Louisiana State University Medical Center spokesman Marvin McGraw. One other victim was in stable condition at the hospital, he said. Seven others had been released. The conditions of other victims were unclear.
Federal investigators say they have no indication that the shooting was an act of terrorism.
"It's strictly an act of street violence in New Orleans," New Orleans FBI spokeswoman Mary Beth Romig said Monday.