A suspect has been arrested after he approached a White House security checkpoint with a firearm on Friday afternoon.
The man was shot by secret service and transported to George Washington University hospital in critical condition.
The secret service put the White House on lockdown immediately after the incident but that was later lifted.
A section of Pennsylvania Avenue, part of 17th Street and Lafayette Square, remained closed to the public, cordoned off by yellow "authorized personnel only" tape. Onlookers were gathering and taking pictures, prompting occasional shouted warnings from the secret service to stay back.
A secret service spokesman, David Iacovetti, said that just after 3pm the man approached the publicly accessible White House entrance at 17th and E Streets with a firearm visible.
"Uniformed division officers gave numerous verbal commands for the subject to stop and drop the firearm," he said. "When the subject failed to comply with the verbal commands, he was shot once by a secret service agent and taken into custody."
A White House official said no one in or associated with the White House was injured and that everyone inside was safe and had been accounted for.
Ranjit Singh, who works near where the incident happened, said he saw a "white guy" with a gun in his right hand approaching police who were yelling at him to drop it.
Barack Obama was not at the White House at the time of the incident. The president had left earlier in the day for the golf course at Andrews air force base in Maryland. Officials have not said how or if Obama was secured after the secret service learned about the shooting incident. Obama has been made aware of the shooting.
Vice-President Joe Biden was in the White House complex at the time and was secured during the lockdown, his office said.
First lady Michelle Obama was wrapping up a speech in downtown Washington at midday on Friday. Her office would not say where she and the Obama daughters
Veteran peace protester Philipos Melaku-Bello, 54, was outside the White House when the panic began. He estimated there were about 250 people and it was just before 3.20pm. "I knew from the immediacy in the secret service’s voice how dire it was," he said.
"Some people were in a panic because when they hear the secret service shouting they know it’s serious. I’m a protester for world peace so it’s too close for comfort."
Melaku-Bello said he has been demonstrating outside the White House for 34 years and evacuations of the public can take place 10 times a week, but ones with "this immediacy" only happen about 15 times a year.
The regular flow of tourists has been abruptly halted. Colleen McKearney, 29, visiting from Seattle, said: "We have no idea what’s happening. We were going to look at the White House. We’ll be patient and come back in a little bit."
Jason Wilson, 45, was lining up for entry to the White House, where he and about 60 other people were due to receive awards for volunteer service, when he heard a gunshot.
"I thought it was a tyre on a truck that exploded," he recalled. "Then I looked at my friend and said, ‘Could that have been a gunshot?’ Then the secret service said, ‘Move! Move!’ They were prompt."
Wilson, founder and chief executive the NGO The Yunion, added: "Of course at the back of your mind you think ‘Could it be a terrorist attack?’ but we were all calm. I’m from Detroit. Just stay calm. What’s there to be scared of?"
