The moment when a gunman opened fire during a Florida video game tournament can be heard in a chilling video that was live-streamed online.

Two people were killed and 11 others were injured when the gunman, 24-year-old David Katz, opened fire Sunday afternoon after reportedly becoming frustrated at losing in the Madden NFL 19 tournament.

Katz then fatally shot himself before police arrived at the Chicago Pizza restaurant at the Jacksonville Landing shopping mall.

WARNING: Video below may be disturbing to watch. 

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The gaming tournament was being live-streamed on Twitch, a popular platform through which members watch others compete.

The video does not show the shooter, but many gunshots could clearly be heard, while a red laser sight - presumed to be from the handgun - was visible on the shirt of one of the victims before the video cut away.

One witness said "everyone [was] running for their lives," and that people were being trampled while trying to exit the venue, while others tried to hide from the shooter.

Twitch tweeted on Sunday that it was "shocked and saddened" by the deadly incident, and it prompted calls for tighter security in future video game tournaments.

Officials swarmed Katz's family's upscale home in Baltimore late on Sunday, but no specifics regarding the investigation have been released.

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