Alleged shooter David Katz, 24, was competing at the video game tournament, and apparently shot at least two people before killing himself. The LA Times reported he had earlier lost in the tournament which was being live streamed when he opened fire.
Police searched on Monday for a motive in the third mass shooting in Florida in two years after a gunman opened fire on Sunday at an online video game tournament as it was being live streamed from a Florida mall, killing at least two people and then fatally shooting himself in an attack that sent several others to hospitals, authorities said.
Jacksonville Sheriff Mike Williams said authorities believe 24-year-old David Katz of Baltimore carried out the attack using at least one handgun at the Jacksonville Landing, a collection of restaurants and shops along the St Johns River.
He said the man died from a self-inflicted gunshot, adding authorities were still making final confirmation of his identity with the FBI assisting them in Baltimore.
The Miami Herald newspaper reported four people were dead and 11 wounded in the shooting at the Madden 19 American football tournament in downtown Jacksonville. Madden is a hugely popular multi-player video game based on the National Football League.
TRT World's Mhairi Beveridge reports.
Sky News Action Jax television station also reported that four people had been killed and 11 others had been wounded.
According to the LA Times, quoting player Steven "Steveyj" Javaruski, a professional Madden player for Noble eSports, the shooter was a gamer who had been competing and lost.
In subsequent tweets, police said they were still searching The Landing entertainment and shopping complex, where the tournament — a regional qualifier for finals in Las Vegas with a $25,000 prize — was being held at the GLHF Game Bar.
They urged people hiding in locked areas of the complex to stay in place and call 911 to make their location known.
In disturbing footage apparently captured as part of a live stream on the video game streaming website Twitch, several gunshots could be heard in the background, before the stream disconnected. Twitch removed the video, but it remained available on social media.
"This is a horrible situation, and our deepest sympathies go out to all involved," Madden's creator, EA Sports, said in a statement.
CompLexity Gaming, one of the gaming teams, said its player Drini Gjoka was grazed on the hand.
"We're obviously shocked and saddened by this afternoon's events. Our player, Drini, was hit in the thumb but is going to be fine. He managed to escape and run down the street to a nearby gym," director Jason Lake said.
"I will never take anything for granted ever again. Life can be cut short in a second," Gjoka tweeted.
Another player, "DubDotDUBBY," said a bullet had grazed his head.
"I feel fine, just a scratch on my head. Traumatized and devastated," he tweeted.
Germany-based SK Gaming also confirmed their player "JoelCP_" was safe.
"Our thoughts are with everyone that had to be part of such a horrendous event," it said.
The professional gamer known as "oLARRY2K," of Bucks Gaming, was said to have been shot in the chest, according to several social media users, including one describing herself as his mother.
TRT World's Steve Mort has more from Florida.
Latest in a series of shootings
Florida has suffered multiple shootings in recent years: 49 people died in a June 2016 attack on a gay nightclub, while 17 were killed at Marjory Stoneman Douglas High School earlier this year.
Florida Senator Marco Rubio said that the FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives were investigating Sunday's shooting.
Florida Governor Rick Scott, meanwhile, confirmed he had offered state support in the aftermath.
White House press secretary Sarah Sanders confirmed President Donald Trump had been briefed on the incident.
"We are monitoring the situation," she said.
The Jacksonville Landing, in the heart of the city's downtown, hosts concerts and other entertainment, has a busy food court and a host of bars and restaurants. President Donald Trump held a rally there in October 2015 early in his campaign for the White House.