A man draped in an American flag climbed over the fence at the White House, prompting a lockdown as the first family celebrated Thanksgiving.

The man was immediately apprehended and taken into custody pending criminal charges, the Secret Service said. The incident took place about 2.45pm local time.

An image of a man on top of a section of fence in front of the North Lawn was posted on the website of television station WJLA.

Another image showed the man standing on the lawn with his arms raised in victory.

Witness Victoria Pena of Houston said the man was standing with other people visiting the White House compound when he rushed toward the fence carrying what appeared to be a binder.

"I just heard him take a big, deep breath and whisper to himself, 'All right, let's do this' and he took off," she said.

"It was chaotic. Everyone around us was yelling and kids were crying. It was pretty unexpected."

Security personnel and guard dogs ran toward the man and he lay on the grass awaiting them, Ms Pena said.

The north and south fence lines at the White House were temporarily closed, Secret Service spokesman Robert Hoback said.

In the hours after the incident, numerous armed security personnel were seen along the streets and pavements outside the executive mansion.

President Barack Obama and his wife and daughters were spending the holiday at the White House.

In May, the Secret Service added a second layer of steel spikes to the top of the fence following an incident the previous month when a California man scaled it and got on to the lawn.

Other long-term security enhancements were under consideration in response to a September 2014 security breach in which a Texas man managed to scale the fence, enter the executive mansion and run deep into the building.

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