The New York City Police Department said that staff at an area hospital pronounced the man dead.
Officials and eyewitnesses said that the man, who was at Collect Pond Park around 1:30 p.m., took out leaflets espousing conspiracy theories, threw them, then doused himself with an accelerant and set himself on fire.
A large number of police officers were nearby when this happened, and some officers and bystanders rushed to help the man, who was taken to hospital in critical condition.
The man, who police said had traveled from Florida to New York in the past few days, did not pass any security checkpoints to enter the park.
The park outside the courthouse was a gathering place for protesters, journalists and tramps throughout Trump’s trial, which began with jury selection on Monday.
During Friday, the streets and sidewalks in the area surrounding the courthouse were generally wide open and crowds were small and largely orderly.
Authorities said they were also reviewing security protocols, including restrictions on entry to the park, with traffic blocked from the side street through which Trump enters and exits the building.
“We may have to close this area,” New York City Police Deputy Commissioner Kaz Daughtry said at a news conference outside the courthouse, adding that officials would discuss the security plan soon.
