There were no immediate reports of deaths, but fire officials in Washington said there were at least some injuries. The U.S. Geological Survey said the quake registered magnitude 5.8 and was centered 40 miles northwest of Richmond, Va.
Two nuclear reactors at the North Anna Power Station, in the same county as the epicenter, were automatically taken off line by safety systems, said Roger Hannah, a spokesman for the U.S. Nuclear Regulatory Commission.
The earthquake came less than three weeks before the 10th anniversary of the Sept. 11 attacks, and in both Washington and New York it immediately triggered fears of something more sinister than a natural disaster. At the Pentagon, a low rumbling built until the building itself was shaking, and people ran into the corridors of the complex. The shaking continued there, to shouts of "Evacuate! Evacuate!"
The Park Service closed all monuments and memorials on the National Mall, and ceiling tiles fell at Reagan National Airport outside Washington. All flights there were put on hold.
In lower Manhattan, the 26-story federal courthouse in lower Manhattan, blocks from ground zero of the Sept. 11 attacks, began swaying, and hundreds of people streamed out of the building.
Workers in the Empire State Building spilled into the streets, some having descended dozens of flights of stairs.
"I thought we'd been hit by an airplane," said one worker, Marty Weisner.
Another, Adrian Ollivierre, a 28-year-old accountant who was in his office on the 60th floor when the quake struck, said: "I thought I was having maybe a heart attack, and I saw everybody running. I think what it is, is the paranoia that happens from 9/11, and that's why I'm still out here -- because, I'm sorry, I'm not playing with my life."
Shaking was felt as far south as Charleston, S.C., and as far north and east as Martha's Vineyard, Mass., where President Barack Obama is taking summer vacation and was starting a round of golf when the quake struck at 1:51 p.m. EDT.
A magnitude of 5.8 would make the quake among the most powerful to strike the eastern United States. In 1897, a magnitude-5.9 quake was recorded at Giles County, Va., the largest on record in that state.
East Coast earthquakes are far less common than in the West, but they tend to be felt over a broad area.
"The waves are able to reverberate and travel pretty happily out for miles," said U.S. Geological Survey seismologist Susan Hough.
Amtrak said its trains along the Northeast Corridor between Baltimore and Washington were operating at reduced speeds and crews were inspecting stations and railroad infrastructure before returning to normal.
More than 12 million people live close enough to the quake's epicenter to have felt shaking, according to the Geological Survey. The agency said put the quake in its yellow alert category, meaning there was potential for local damage but relatively little economic damage.
The USGS said the quake was 3.7 miles deep.
The Virginia quake came a day after an earthquake in Colorado toppled groceries off shelves and caused minor damage to homes in the southern part of the state and in northern New Mexico. No injuries were reported as aftershocks continued Tuesday.
In Charleston, W.Va., hundreds of workers left the state Capitol building and employees at other downtown office buildings were asked to leave temporarily.
"The whole building shook," said Jennifer Bundy, a spokeswoman for the state Supreme Court. "You could feel two different shakes. Everybody just kind of came out on their own."
In Ohio, where office buildings swayed in Columbus and Cincinnati and the press box at the Cleveland Indians' Progressive Field shook. At least one building near the Statehouse was evacuated in downtown Columbus.
In downtown Baltimore, the quake sent office workers into the streets, where lamp posts swayed slightly as they called family and friends to check in.
Social media site Twitter lit up with reports of the earthquake from people using the site up and down the U.S. 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-tall 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."