Numerous injuries were reported but no deaths or serious injuries.
All the memorials and monuments on the National Mall in Washington were evacuated. Parts of the Pentagon, White House and Capitol were evacuated.
President Barack Obama led a conference call on the earthquake with top administration officials, including his homeland security secretary, national security adviser and administrator of the Federal Emergency Management Agency.
He was told there were no reports of major infrastructural damage.
The quake was felt along the East Coast to Martha's Vineyard, the Massachusetts island where Mr Obama is on holiday.
The US Geological Survey said the earthquake was half a mile deep and centred near Louisa, Virginia, about 40 miles north-west of Richmond.
Shaking was felt as far south as Charleston, South Carolina.
The National Cathedral in Washington appeared to be damaged.
A spokesman for the cathedral said at least three of the four pinnacles on the central tower fell off and the central tower appeared to be leaning.
Two nuclear reactors at the North Anna Power Station in the same county as the epicentre were automatically taken off line by safety systems around the time of the earthquake, said Roger Hannah, a spokesman for the US Nuclear Regulatory Commission.
The Dominion-operated power plant is being run off four emergency diesel generators, which are supplying power for critical safety equipment.
Mr Hannah said the agency was not immediately aware of any damage at nuclear power plants in the south east.
Mr Obama and many of the nation's leaders were out of town on holiday when the quake struck at 1:51 pm local time.
The shaking was felt on the Martha's Vineyard golf course as Mr Obama was just starting a round.
Nearly two hours after the quake struck, the White House was unable to say whether the president felt the ground sway. But reporters travelling with him said immediately that they had felt it.
At the Pentagon in northern Virginia, a low rumbling built to the point that the building was shaking. People ran into the corridors of the government's biggest building and as the shaking continued there were shouts of "Evacuate! Evacuate!"
The US Park Service evacuated and closed all National Mall monuments and memorials.
At Reagan National Airport outside Washington, ceiling tiles fell during a few seconds of shaking. Authorities announced it was an earthquake and all flights were put on hold.
Amtrak said its trains along the north east corridor between Baltimore and Washington were operating at reduced speeds and crews were inspecting stations and railroad infrastructure before returning to normal.
In New York, the 26-story federal courthouse in lower Manhattan began swaying and hundreds of people were seen leaving the building. Court officers were not letting people back in.
More than 12 million people live close enough to the quake's epicentre to feel shaking, according to the US Geological Survey.
East Coast earthquakes are far less common than in the West, but they tend to be felt over a broad area. That is because the crust is not as mangled and fractured, allowing seismic waves to travel without interruption.
"The waves are able to reverberate and travel pretty happily out for miles," said US Geological Survey seismologist Susan Hough.
Social media site Twitter lit up with reports of the earthquake from people using the site up and down the US eastern seaboard.
"People pouring out of buildings and onto the sidewalks and Into Farragut Park in downtown DC ...," tweeted Republican strategist Kevin Madden.
John Gurlach, air traffic controller at the Morgantown Municipal Airport was in a 40-foot tower when the earth trembled.
"There were two of us looking at each other saying, 'What's that?"' he said, even as a commuter plane was landing. "It was noticeably shaking. It felt like a B-52 unloading."
Immediately, the phone rang from the nearest airport in Clarksburg, and a computer began spitting out green strips of paper - alerts from other airports in New York and Washington issuing ground stops "due to earthquake."
The Dominion-operated power plant is being run off four emergency diesel generators, which are supplying power for critical safety equipment.
Nuclear Regulatory Commission spokesman Roger Hannah says the agency was not immediately aware of any damage at nuclear power plants in the south east. The NRC and Dominion are sending people to inspect the site.
Hanna said he knows of no other reactor shutdowns but that unusual events were reported at a dozen other plant sites.
In Washington, a District of Columbia fire department spokesman said there were numerous injuries but so far there no reports of serious injuries or deaths.
Pete Piringer says numerous buildings have been damaged, including the Ecuadorian embassy and a handful of schools.
He says thousands of people are milling about in the city centre after evacuating their buildings.
All city fire engines and ambulances have been deployed.
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