The suspect died after a vehicle pursuit with officers who fired at him. The victims - who ranged in age from one to about 14 - included children related to the gunman, said Shreveport Police Department spokesperson Chris Bordelon.
Investigators did not say what may have set off the attack.
The mass shooting on Sunday, US time, was the deadliest in America in more than two years.
"This is an extensive scene unlike anything most of us have ever seen," Bordelon said.
Officers fired at the suspect during a chase after he carjacked a vehicle at gunpoint while leaving the scene, Bordelon said.
Police said the attacks began in a neighbourhood south of downtown Shreveport when the suspect shot a woman at one home and then drove to the other location where the "heinous act" was carried out.
State Representative Tammy Phelps said some children tried to escape out the back door.
"I can't even imagine what the police officers, first responders actually dealt with when they got here today," she said at a news conference.
Authorities did not release the name of the gunman but did say he was an adult male.
Liza Demming, who lives two houses down from where most of the victims were shot, said her security camera captured video of the suspect running away along with the sound of two shots.
"That's pretty much all I saw, was him running out of the house and the cars leaving," she said.
Demming later went outside and saw the covered body of a child on the home's roof. She said she did not know the gunman's name.
"He looks like the dad that comes over here," she said, adding that he was just with the children a few days ago.
Pastor Marty T Johnson Sr, of a nearby Baptist church, who owns one of the homes where the shootings occurred, said a person who works for him had rented it to the family, but he never had dealings with them.
"I don't really know them, I really don't," he said. "I do plan on having a prayer vigil for the family, and anything I can do, with so many children, to help them bury the children, I'm going to do so."
The Caddo Parish Coroner's Office released a statement on Sunday saying it was not yet releasing any of the children's names because identification of the victims was pending.
Police said two women who were shot and wounded were being treated for serious injuries.
It was the deadliest mass shooting in the US since eight people were killed in a Chicago suburb in January 2024, according to a database maintained by The Associated Press and USA Today in partnership with Northeastern University.
At a news conference outside the residence where one of the shootings occurred, officials appeared stunned, requesting patience and prayers from the community as they sorted through multiple crime scenes.
"I just don't know what to say, my heart is just taken aback," Shreveport Police Chief Wayne Smith said. "I cannot begin to imagine how such an event could occur."
"This is a tragic situation - maybe the worst tragic situation we've ever had," said Tom Arceneaux, mayor of the city in northwestern Louisiana with about 180,000 residents. "It's a terrible morning."
Louisiana Governor Jeff Landry and US House Speaker Mike Johnson, who is from Shreveport, said in separate statements they were heartbroken and praised law enforcement for their response.
"We're holding the victims, their families and loved ones, and our Shreveport community close in our thoughts and prayers during this incredibly difficult time," Johnson said in a statement.
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