A woman and a man have died and two people are in critical condition after a lightning strike near the White House last night, police in the US capital said.
The lightning hit Lafayette Square, a small park across the street from the White House, shortly before 7pm last night, leaving two men and two women with "critical life-threatening injuries," according to a statement from Washington's fire and emergencies department.
All the victims were taken to local hospitals, but on Friday morning the Metropolitan Police confirmed that two of them - 75-year-old Donna Mueller and 76-year-old James Mueller, both from Janesville in Wisconsin - had been pronounced dead.
The other two adults remain in critical condition, police said.
A White House spokeswoman said the Biden administration was "saddened by the tragic loss of life."
"We are praying for those still fighting for their lives," added Press Secretary Karine Jean-Pierre in a statement.
US Secret Service and park police rushed to help the four after witnessing the strike, fire and emergency services department spokesman Vito Maggiolo said in a statement posted on social media.
Photos posted by the department on social media showed multiple ambulances and at least one fire truck with flashing lights working at the scene.
The victims are believed to have sought shelter from the storm under one of the park's trees, and Mr Maggiolo warned that this was "a very dangerous place to be".
"Trees are not safe places," Mr Maggiolo told the Washington Post.
Witness David Root told NBC he heard a "horrific boom."
"I just couldn't believe it," he was quoted as saying. "Was surreal. I have never seen anything like this in my entire life."
He said he had been sheltering beneath a tree when he saw the lightning strike across the park.
The people "weren't moving," he said, so he and others ran over to give help.
The Washington Post said the four were found some 100 feet from the statue of former US president Andrew Jackson which marks the center of the square.
The strike was part of a severe thunderstorm that hit the American capital on Thursday evening.
"Trees are not safe places," Mr Maggiolo told the Post.
"Anybody that goes to seek shelter under a tree, that's a very dangerous place to be."