WASHINGTON (AP) — A man set himself on fire on the National Mall in the nation's capital as passers-by rushed over to help put out the flames, officials and witnesses said Friday afternoon.

The reason for the self-immolation was not immediately clear and the man's identity was not disclosed. But it occurred in public view, on a central national gathering place, in a city still rattled by a mass shooting last month and a high-speed car chase outside the U.S. Capitol on Thursday that ended with a woman being shot dead by police with a young child in the car.

The man on the Mall suffered life-threatening injuries and was airlifted to the hospital, said District of Columbia fire department spokesman Tim Wilson.

He was standing by himself in the center portion of the Mall when he emptied the contents of a red gasoline can on himself and set himself on fire moments later, said Katy Scheflen, who witnessed it as she walked across the area. Police say they responded around 4:20 p.m. Friday.

Scheflen said the man was clearly alive as the fire spread, and passing joggers took off their shirts in an effort to help put out the flames. It was not clear who actually extinguished the flames.

A police department spokesman said the man was conscious and breathing at the scene. MedStar Washington Hospital Center tweeted that the man was taken there and he was in critical condition Friday night.

"There was not a lot people could do because it was a gasoline fire," Scheflen said.

She said he may have said something before he acted "but it was nothing intelligible." She said she did not see him holding any signs before he set himself ablaze.

She said there was another man with a tripod set up near him, but it's unclear if the man was filming the incident.

Lt. Pamela Smith of the U.S. Park Police, which is investigating along with the D.C. police department, said: "I'm not aware of any signage or any articulation of any causes."

The D.C. police department has dispatched its violent crimes branch, which responds to cases in which a person suffers serious injury.