A man set himself on fire on Friday afternoon near the Lower Manhattan courthouse where jurors were being chosen for the criminal trial of former President Donald J. Trump.

The man, who had lingered outside the Manhattan Criminal Courthouse earlier this week, doused himself with accelerant at around 1:35 p.m. in Collect Pond Park, across the street from the building. Onlookers screamed and started to run, and soon, bright orange flames engulfed the man. He threw leaflets espousing anti-government conspiracy theories into the air before setting himself on fire.

People rushed and tried to put out the flames, but the intensity of the heat could be felt from some distance.

After a minute or two, dozens of police officers arrived, running around and climbing over barricades to extinguish the blaze.

The man was loaded into an ambulance and rushed away.

The authorities said he was taken to a hospital burn unit in critical condition and was unlikely to survive.

City officials identified the man as Max Azzarello, 37, of St. Augustine, Fla. Mr. Azzarello had appeared outside the courthouse on Thursday, holding a sign displaying the address of a website where the same pamphlets were uploaded. The top post of the website says, “I have set myself on fire outside the Trump Trial.”

Mr. Azzarello walked around Lower Manhattan earlier in the week, holding a sign on Wednesday critical of New York University at Washington Square Park before moving on Thursday to Collect Pond Park.

At the park on Thursday, Mr. Azzarello had held up various signs and at one point shouted toward a group of reporters gathered there, “Biggest scoop of your life or your money back!” One of his signs claimed that Mr. Trump and President Biden were “about to fascist coup us.”