A man has set himself on fire outside the court in Manhattan where former President Donald Trump's hush-money trial is being held, reports BBC.
The man doused himself in a liquid before throwing conspiracy-theory pamphlets into the air, police said.
His motive is unknown and police responded to the scene.
Mr Trump was in the building to attend jury selection, where he has had a security detail, but the former president left during the incident.
Emergency officials said that court security had not been breached in the incident. The case, which had just completed alternate jury selection, resumed later in the afternoon. Opening statements are expected to begin on Monday.
In a news conference, investigators said they had received a 911 emergency call at around 13:30 local time (18:30 BMT) telling them that a man had lit himself on fire.
They identified him as Maxwell Azzarello, 37, who had arrived in New York from his home in Florida sometime in the past week. He has no criminal record in New York, and his family in Florida were unaware that he had travelled to the city.
New York Police Chief Jeffrey Maddrey said Mr Azzarello was seen "shuffling around" in the park before reaching into a bag for the flammable liquid and pamphlets.
The pamphlets were "propaganda-based", said Chief Maddrey, adding that they were regarding a "conspiracy theory".
There was a massive police presence outside the courthouse because of the trial, and officers quickly ran into the park shouting for a fire extinguisher. Mr Azzarello was carried away on a stretcher, his body badly burned. The police said he was taken to a hospital burn centre in critical condition.
Witness Julie Berman told reporters: "It was hot, and it didn't make a lot sense. The whole thing happened so fast... it took me like 20 seconds to figure out what was going on."
NYPD investigators were later seen collecting pamphlets that Mr Azzarello had scattered before self-immolating. They have deemed the area safe.
Investigators are still interviewing witnesses and said he didn't appear to say anything before setting fire to himself.
Three NYPD officers and one court officer had minor injuries after helping to extinguish the blaze.
Officials said they will now reassess security outside the court.