None of the names of the dead or injured had been released by the New Orleans Police Department.
Police are expected to hold a press conference late on Saturday evening.
One victim was in critical condition Sunday morning.
Three of the seven injured people were taken by ambulance to University Medical Center's trauma center, police said. "A lot of people saw and heard what happened", Harrison said in asking for assistance in solving the crime.
"We believe they actually stood over one of the individuals and fired multiple rounds and then after that fled", Harrison told local media. Seven other victims - five men and two women - were taken to two separate hospitals.
It is understood at least 10 people have been shot in a "gang-related" attack.
Near the scene of the shooting, beyond the police tape, people could be seen crying and hugging one another in comfort.
The three deceased were described as two men and one woman.
New Orleans Mayor LaToya Cantrell said in a statement that authorities will focus "every resource necessary to ending this horror and seeing justice done".
"I speak for everyone in our city when I say we are disgusted and infuriated, and we have had more than enough", she wrote.
NOLA.com reported New Orleans Police Michael Harrison indicated one of the suspects used a handgun and the other used a rifle and both "appeared to fire indiscriminately".
In October 2011, the younger brother of John Matthews, who owned Jazz Daiquiris at the time, was gunned down three days after Hankton was given a life sentence in the 2008 shooting.
Rangers send Cole Hamels to Cubs in trade
The Rangers will receive right-hander Eddie Butler , right-handed prospect Rollie Lacy , and a player to be named in return. The pitchers were Rangers teammates before Darvish was traded to the Los Angeles Dodgers and later signed by the Cubs.