Videos shared to social media showed a person engulfed in flames, the fire subsequently being put out.
Authorities from the National Park Service and US Park Police were administering first aid after the incident on the Ellipse near the Washington Mall, an area popular with tourists, according to a Twitter post. Further details were not available.
It was the second such incident since April 12, when a man in a wheelchair-type electric scooter lit his jacket on fire outside the White House fence.
That man was hospitalized with what appeared to be non-life threatening injuries, the US Secret Service said.