Police have named the shooter as 24-year-old David Katz from Baltimore, Maryland. (AFP)

Top figures from the professional US online gaming community expressed shock and dismay on Sunday after a shooting at a tournament in Florida left three people dead.

The rampage took place at the GLHF Game Bar in downtown Jacksonville, which was livestreaming a regional qualifier for a new football video game, Madden NFL 19.

Police named the shooter as 24-year-old David Katz from Baltimore, Maryland, and said he was in Jacksonville for the competition. They said he killed two people before taking his own life, but declined to comment on his motive.

The killings rocked the world of professional electronic gaming, also known as esports, which boasts an estimated 250 million players worldwide in a growing market worth about a billion dollars a year.

"My heart goes out to the family, friends and people affected by the madden shooting today," one video platform streamer and Internet personality, Ninja, wrote on Twitter. "Evil times we live in, just need to out shine that evil with positivity."

Another high profile gamer, @ProblemWright, one of the top names in Madden competitions according to its maker, Electronic Arts Inc, said he was crying and "in so much pain."

"All over a videogame. Two of our brothers are gone man and its so disturbing. One of the most tragic days ive experienced. This community is like family. Broken," he wrote on Twitter.

Cloud9, a professional gaming organization based in Los Angeles, California, said it was deeply saddened and shocked by the tragic events: "Our hearts and deepest condolences go out to the victims, families, and all those affected by today's violence," the organization said on Twitter. "Stay safe."

The victims have not yet been officially named, but another professional Madden player, @ThePrxdigyy, tweeted photos of two gamers who were reported on social media to have been killed.

"RIP to two of our brothers and speedy recovery for the others injured," he wrote. "Love you all and hope something like this never happens again."

Marquis Williams said he traveled from Chicago with his girlfriend to attend the competition.

"I just can't wrap my head around the fact we were here traveling just to play video games, something that we love to do, and it's just sad that lives were lost because of it," Williams told reporters at the scene.

© Thomson Reuters 2018