A gunman killed four people and wounded several others when he opened fire at a video game tournament that was being streamed online from a bar in Jacksonville, Florida.
Jacksonville Sheriff Mike Williams said one white male suspect was dead at the scene.
He declined to comment on what led to the third major mass shooting in Florida in the last two years.
Dozens of ambulances and police cars flooded into The Jacksonville Landing, a waterfront dining, entertainment and shopping site in the city’s downtown, after several shots rang out on a sunny Sunday afternoon.
The shooting took place during a regional qualifier for the Madden 19 online game tournament at the GLHF Game Bar inside a Chicago Pizza restaurant, according to the venue’s website.
The bar was livestreaming the competition when the gunfire started, according to video of the stream 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.
No official casualty figures were available, but local media reported that at least four people are dead and more than 10 injured.
Sheriff Williams told a media conference the suspected shooter’s identity was yet to be determined.
He said the scene had been cleared and declared safe, but asked people to keep away from the area.
Ryan Aleman, who was at the bar, told CNN that he saw “at least six bodies on the floor” of people who had been shot.
Police earlier advised those hiding inside the bar and nearby restaurants to wait to be rescued.
“We are finding many people hiding in locked areas at The Landing,”the sheriff’s office said via Twitter.
“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,” it said.
The sheriff’s office earlier took to Twitter and Facebook to warn people to stay away from Jacksonville Landing.
The department told people to “stay far away from the area. The area is not safe at this time. STAY AWAY.”
— Jax Sheriff's Office (@JSOPIO) August 26, 2018
The sheriff’s office did not provide any other information, but separately advised news media to stay away from the area, which contains restaurants and shops along the St. Johns River.
An online stream of the Madden 19 event, several loud gunshots can be heard and the game abruptly stops.
Watch the Madden 19 stream below (warning: disturbing audio):
Sheriff Williams said investigators were examining the footage, and appealed for any witnesses with video of the tournament or shooting to come forward.
Complexity Gaming team posted that one of its players, Young Drini, was grazed on the hand in the shooting, but was safe.
“I am literally so lucky. The bullet hit my thumb.” Drini said in a separate post.
Ryan Alemon, who travelled from Texas to participate in the tournament, said he ducked down and ran toward the restroom when he heard the gunshots, hiding there for about 10 minutes before running from the venue.
Jacksonville Landing is an open-air marketplace featuring stores, bars and restaurants in the centre of Jacksonville, Florida.
Malik Brunson was at a nearby Hooters restaurant when the shooting occurred.
“All I heard was he got a gun and the shooting started,” Mr Brunson told CNN.
“One of the men ran into Hooters with the shot wounds, they locked us in the restaurant,” he was quoted as saying.
US President Donald Trump has been briefed on the situation, White House press secretary Sarah Huckabee Sanders said.
Federal law enforcement officials were monitoring the situation, with the Bureau of Alcohol, Tobacco, Firearms and Explosives responding to the scene.