Everything we know about the deadly mass shooting at a Florida video game tournament.

WARNING: The following contains audio and video which may be distressing. Reader discretion is advised.

An NFL video game plays out on the screen. In the corner, a small picture-in-picture box shows the two men clutching controllers, their smiling faces lit by the glow of the displays in front of them.

A laser is seen briefly flashing across one man’s chest. The box featuring the two men disappears and the game takes over the full screen. Seconds later comes a sharp cracking sound, followed by 11 more.

People can be heard yelling, screaming in the background, as a message flashes up on the screen. ‘Controller disconnected.’

This disturbing footage, shared on social media, reportedly captures the moment a gunman opened fire on a live-streamed video game tournament at a shopping complex in Jacksonville, Florida, killing at least four people and injuring several more.

Here’s what we know so far.

Disturbing video/audio is being posted on social media following a “mass shooting” in Jacksonville.
**WARNING: This video/audio may be disturbing for some viewers** #TheLandingMassShooting pic.twitter.com/JKcQFUi3sU

— CBS 4 News (@kgbt) August 26, 2018

How the shooting unfolded.

The shooting took place on Sunday, local time, during a regional qualifier for the Madden 19 online game tournament at the GLHF Game Bar at The Jacksonville Landing, a waterfront dining, entertainment and shopping site in the city’s downtown.

Police are yet to report a motive for attack, but according to The Los Angeles Times, the suspected gunman had competed in the tournament and lost. He has yet to be identified but has been described as a white male.

Citing messages from another player in the room, the paper said the gunman appeared to target several victims before taking his own life.

After the incident, law enforcement flooded and into barricaded a three-block radius around the mall, while police and Coast Guard boats patrolled the nearby river.

The Jacksonville Sheriff’s Office said its deputies were finding many people hiding in locked areas at the waterfront precinct.

“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.”

At least three people injured in the shooting were transported to Jacksonville’s Memorial Hospital and all are in stable condition, hospital spokesperson Pete Moberg told CNN.

One person is being treated for a minor injury at Baptist Medical Center, spokesperson Cindy Hamilton said.

A Twitter user named Drini Gjoka said he was taking part 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.”

Footage of the shooting.

Footage of the live-streamed event that appears to capture audio of the shooting was shared to social media.

While two competitors can been seen in the clip, the footage returns to the video game moments before gunfire can be heard.

Some viewers claim a thin, laser-like beam that appears to flick across one of the men's chests may emanate from the shooter's weapon.

History repeating.

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.

Florida Governor Rick Scott said he had offered the Jacksonville Sheriff's Office any state resources it needed.

Madden 19 maker Electronic Arts 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.

-With AAP