A shooter killed two people and wounded 10 others on Sunday at a video game tournament that was being streamed online from a restaurant in Jacksonville, Florida, local media said citing police sources.
The Jacksonville Sheriff's Office said a suspect was dead at the scene. "Searches are being conducted," it said on Twitter.
Police confirmed three people have died in the shooting, one of them was the suspect.
He has been identified as David Katz from Maryland.
Emergency crews and law enforcement flooded into The Jacksonville Landing, a waterfront dining, entertainment and shopping site in the city's downtown.
The shooting took place during a regional qualifier for the Madden 19 online game tournament at the GLHF Game Bar inside a Chicago Pizza restaurant, according to the venue's website.
It was livestreaming the tournament when several shots rang out, according to video of the stream shared on social media. In the video, players can be seen reacting to the gunfire and cries can be heard before the footage cuts off.
One Twitter user, Drini Gjoka, said he was in the tournament and was shot in the thumb.
"Worst day of my life," Gjoka wrote on Twitter. "I will never take anything for granted ever again. Life can be cut short in a second."
The Los Angeles Times reported the shooter was a gamer who was competing in the tournament and lost. Citing messages from another player in the room, the Times said the gunman appeared to target several victims before killing himself. Reuters could not immediately confirm that account of events.
The Florida shooting occurs amid a debate about US gun laws that was given fresh impetus by the massacre in February of 17 people at a high school in Parkland, Florida.
Two years ago a gunman killed 49 people at the Pulse nightclub in Orlando.
The sheriff's office said many people were transported to hospital, and its deputies were finding many people hiding in locked areas at The Landing.
"We ask you to stay calm, stay where you are hiding. SWAT is doing a methodical search," it said on Twitter. "We will get to you. Please don't come running out."
A spokesman for Jacksonville's Memorial Hospital, Peter Moberg, said it was treating three victims, all of whom were in stable condition.
Florida Governor Rick Scott, a Republican who is challenging longtime Democratic Senator Bill Nelson in November's election, said he had offered to provide local authorities with any state resources they might need.
Florida Senator Marco Rubio said both the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives were coordinating with local authorities to provide assistance.
President Donald Trump has been briefed and is monitoring the situation in Jacksonville, the White House said.
Reacting to news of the shooting during the tournament involving its video game, Madden 19 maker Electronic Arts Inc said it was working with authorities to gather facts.
"This is a horrible situation, and our deepest sympathies go out to all involved," the company said on Twitter.