Police in Florida are continuing to search for a motive in the third mass shooting in the US state in two years.

Two people were killed and 11 wounded in Jacksonville after a man opened fire at a video game tournament yesterday.

Witnesses told local media that the gunman, identified by police as David Katz, 24, of Baltimore, was a disgruntled gamer, angry because he lost the tournament.

It was not clear if he knew his victims. Katz took his own life after the attack.

While police have not identified the victims, family members told Jacksonville CBS television station WJAX that the two people killed were Eli Clayton and Taylor Robertson, both were video game contestants.

The Jacksonville Sheriff's office said 11 other people were wounded by gunfire and at least two others were injured while fleeing the scene.

Police say Katz killed himself and his body was found near the bodies of the other victims at The Landing, a popular shopping and restaurant spot in Jacksonville.

Jacksonville Sheriff Mike Williams declined to comment on possible reasons for the attack.

Police and FBI agents swarmed Katz's townhouse in South Baltimore last night, multiple media accounts said, including the Baltimore Sun.

Police also seized Katz's vehicle parked nearby the tournament site.

The shooting took place during a regional qualifier for the Madden 19 online game tournament at the GLHF Game Bar inside a pizza restaurant, according to the venue's website.

The winners of the contest go forward to the video game finals in Las Vegas and compete for $165,000.

The latest shooting occurred amid a debate over 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.

US President Donald Trump has been briefed and is monitoring the situation in Jacksonville, the White House said.

The bar was live streaming a football video game competition when the gunfire started, according to video shared on social media.

In the video, players can be seen reacting to the shots and cries can be heard before the footage cuts off.

The sheriff's office said many people were transported to hospital, and its deputies found many others hiding in locked areas at The Landing.

A spokesman for Jacksonville's Memorial Hospital said it was treating three victims, all of whom were in stable condition.

Reacting to news of the shooting during the tournament involving its game, Madden 19 maker Electronic Arts Inc said it was working with authorities to gather facts.

"The tragic situation that occurred Sunday in Jacksonville was a senseless act of violence that we strongly condemn," a company spokesperson said.