A lone gunman opened fire Sunday during a Madden NFL 19 video game tournament at a Jacksonville restaurant, killing multiple people.

The event at The Chicago Pizza at Jacksonville Landing was being livestreamed on the internet when the gunfire broke out.

Authorities say that at last least nine have been shot and three were killed, including the lone gunman, David Katz, 24, of Baltimore.

Two others were injured fleeing the shooting but were not shot by Katz’s handgun.

All the victims treated at local hospitals are in stable condition, authorities reported.

Ed Buice, the spokesman for the Naval Criminal Investigative Service, told Navy Times Sunday evening that there’s “no known DoD nexus in the Jacksonville incident" for the victims or the dead shooter.

At a 7:20 p.m. Sunday news conference, Duval County Sheriff Mike Williams also told reporters that detectives did not believe Katz had an accomplice and likely spent the evening before the shooting at a local motel.

The Coast Guard patrols the St. Johns River outside The Jacksonville Landing in Jacksonville, Fla., on Sunday. (Laura Heald/AP)
The Coast Guard patrols the St. Johns River outside The Jacksonville Landing in Jacksonville, Fla., on Sunday. (Laura Heald/AP)

Williams said that Katz was believed to have been a participant in the Madden tournament.

FBI agents in Baltimore are assisting Florida investigators there, Williams said.

Earlier, Williams' office took to the social media site Twitter to warn citizens away from the shooting.

“We are 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 inside The Landing. We will get to you. Please don’t come running out,” the sheriff’s office tweeted.

U.S. Coast Guard patrol boats from the Jacksonville Sector rushed to the Landing, a popular mall, and they have established a security perimeter along the St. Johns River.

Investigators are analyzing the online footage of the incident to see if a red dot — the telltale sign of some laser reflex sighted firearms — appeared on the chest of one of the game players shortly before sounds of gunfire could be heard.

Navy officials began an area-wide muster to account for all personnel.

“The muster is underway right now as all area commands are working to account for their people,” said Bill Dougherty, spokesman for Navy Region Southeast. “We have no knowledge at this time whether any of our people were present or have been impacted by this tragedy and are accounting for our people.”

The Jacksonville area is one of the Navy’s four major fleet concentration areas, with commands at Naval Station, Mayport; Naval Air Station, Jacksonville; and Naval Submarine Base, Kings Bay, Georgia.

Virtual musters are routinely conducted by the Navy to practice accounting for military, civilian and family members after natural disasters or man-made crises, Dougherty said.

Sailors are required to maintain updated recall numbers with their commands. During hurricanes, when personnel and their families often scatter to evacuate from the storm, these musters can take days to complete.

Dougherty said he didn’t know how long Sunday’s muster will the Navy will continue the effort until everyone has been contacted.

Police have barricaded a three-block radius around the popular mall, the Associated Press and other media outlets reported.

AP also reported that President Donald Trump called Florida Gov. Rick Scott, offering any federal help necessary to respond to the shooting.