WASHINGTON (AFP) - A man who set himself on fire on the National Mall in the US capital has died, police said on Saturday.

The victim, who suffered from "significant burns throughout his body" died before 9pm (9am Singapore time) Friday, Washington Metropolitan Police spokesman Araz Alali told AFP.

Authorities have yet to identify the individual due to the severity of his burns and an investigation is ongoing, Mr Alali said.

He was unable to comment on reports that the individual had doused himself in gasoline.

The incident unfolded on Friday afternoon when police responded to reports that a man had self-immolated on the grassy esplanade that stretches from the US Capitol to various national monuments and museums.

The man was semi-conscious and breathing when police arrived around 4.30pm and was airlifted by US Park Police to a local hospital.

Washington tourist Meghan Van Heertum, 29, was standing nearby.

"Somebody extinguished the flames. I saw a cop run to his truck and grab a cooler full of ice, grabbed bottles of water, ran back over," she said.

"There were some guys without their shirts on and I heard from some people that this man had set himself on fire, bystanders took off their shirts to put out the fire." The incident comes in the wake of recent events that have sent jitters through the US capital.

On Thursday, a 34-year-old woman led police on a high-speed car chase from the White House to near the US Capitol before being shot dead.

Just weeks earlier on Sept 16, a gunman slaughtered 12 people at Washington's Navy Yard in the nation's latest mass shooting.