The U.S. Geological Survey said the earthquake was half a mile deep. Shaking was felt at the White House and all over the East Coast, as far south as Chapel Hill, N.C. Parts of the Pentagon, White House and Capitol were evacuated. There were no immediate reports of injuries.
It was centered near Louisa, Va., which is northwest of Richmond and south of Washington.
Obama and many of the nation's leaders were out of town on August vacation when the quake struck at 1:51 p.m. EDT. The shaking was felt on the Martha's Vineyard golf course as Obama was just starting a round.
The East Coast gets earthquakes, but usually smaller ones and is less prepared than California or Alaska for shaking.
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.
At the Pentagon in northern Virginia, a low rumbling built and 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!"
In New York, the 26-story federal courthouse in lower Manhattan began swaying and hundreds of people were seen leaving the building. Court officers weren't letting people back in.
The 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.
"did you feel earthquake in ny? It started in richmond va!" tweeted Arianna Huffington, president and editor-in-chief of the Huffington Post Media Group.
Missouri Sen. Claire McCaskill tweeted that her staff in Washington was in an "emergency location. Hope everyone is ok."
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."