Gunfire at a large, outdoor event in Brooklyn killed one man and injured at least 11 others late Saturday night, police said.

Mayor Bill de Blasio tweeted early Sunday morning that the shooting in the east Brooklyn neighborhood of Brownsville “shattered a peaceful neighborhood event.”

A New York City police spokesman said around 3:30 a.m. Sunday that 12 people had been shot, including a 38-year-old man who was dead on arrival at a local hospital. Police said the man was shot once in the head. The spokesman did not know the man’s identity.

No arrests have been made, and police did not offer any details about possible suspects. Police did not have details regarding the conditions of the other 11 people injured and said the investigation was ongoing, as of 4:15 a.m.

At least six people had been transported to local hospitals by just after midnight, with some in serious condition, a New York City fire department spokesman said earlier. He described the scene at the time as “fluid.”

De Blasio’s tweet didn’t include details about the community event, but a notice on the NYC Parks website said programming at the Brownsville Recreation Center next to the playground was canceled because of this weekend’s annual Old Timers Event.

A 2010 newsletter from the parks department described it as a celebration of “former members of the center who went on to success and fame in sports and other endeavors” that’s grown to include concerts and other events. A flyer for the dayslong celebration said Saturday’s event was to begin at 6 pm on Hegermen Avenue, in the vicinity of the site of the shooting.

Calls and emails to the councilmembers organizing the celebration were not immediately returned.

A man who answered a phone number listed online for one of Saturday’s scheduled performers, The Legendary Intruders, identified himself as bandmember Khalil Shabazz. He said his band had already performed and departed the venue before the shooting.

Videos posted on social media showed police clearing large groups of people out of the area around the recreation center following the shooting. Photos from local news outlets showed several people taken from the scene on stretchers, including some with what appeared to be minor wounds.

Brownsville is a neighborhood that’s continued to struggle with gun violence, even as New York has seen its streets get safer than they have been in decades.

“We will do everything in our power to keep this community safe and get guns off our streets,” de Blasio tweeted.

State Sen. Roxanne J. Persaud echoed de Blasio, adding the hashtags ”#StopTheViolence” and ”#PutDownTheGuns” to her tweets expressing frustration with the shooting, which she called “unacceptable” and “cowardly.”

“Our community mourns again. We should be able to have fun in open spaces without fear of violence,” tweeted Persaud, whose district includes Brownsville. “Respect your community. We are better than the violence.”