The eastern seaboard rarely experiences earthquakes and many workers were bewildered -- and feared the worst -- as their desks swayed violently and their ceilings and walls vibrated with ominous intensity.
In a region about to relive the trauma of 9/11 on the 10th anniversary of the Al-Qaeda attacks, many suspected terrorism as they raced down stairways to parks and street corners on a thankfully pleasant summer afternoon.
"I was in the street when the ground shook and I looked up to see the building shaking like a tuning fork," Mary Daley told AFP in New York. Thousands of workers fled office buildings and poured onto the streets of Manhattan to be herded by police towards open areas, trying in vain to use overloaded cell phone services to contact loved ones.
In a bizarre legal twist, the quake prompted the early closure of courthouse offices, meaning former IMF chief Dominique Strauss-Kahn had to wait until Wednesday to collect his passport and leave the country after sexual assault charges against him were dropped.
Fatima Richardson, 28, who was sitting on the steps of New York's state courthouse on her lunch break, told AFP: "You could see the building moving. I was just freaking out."
The 5.8-magnitude quake, which lasted 20-30 seconds and whose epicenter was 3.7 miles (six kilometers) under the small and aptly-named Virginian town of Mineral, was felt as far away as Boston and even in parts of Canada.
The Pentagon, the US Capitol and the historic monuments of the capital were all evacuated and airports suffered delays, but the damage was restricted to only a handful of buildings and there were no reports of casualties.
President Barack Obama was not at the White House and did not feel the quake as he was playing golf some 500 miles (800 kilometers) away in tranquil Martha's Vineyard off the coast of Massachusetts. But people as far away as Ottawa, Canada to the north and Atlanta, Georgia to the south did report feeling the temblor, as did residents in the midwestern US states of Indiana and Michigan. Scientists said the harder, more brittle quality of the ground explained why rare tremors on the east coast are often felt over an area many times bigger than those of a similar magnitude on the more quake-prone west coast. The temblor also hit as emergency officials warned that Hurricane Irene, which was roaring through the Atlantic, may strike the eastern US seaboard this weekend.
Briefed by his aides, Obama was told "there are no initial reports of major infrastructure damage, including at airports and nuclear facilities," said deputy White House spokesman Josh Earnest.
In Washington, the National Cathedral lost part of its towering neogothic spires and suffered cracks in its flying buttresses after the quake struck at 1751 GMT.
Traffic in and around the capital was gridlocked and rail services were slowed, but DC fire and emergency spokesman Pete Piringer said there were no reports of serious damage or injuries.
Near the epicenter in Virginia, the 1,800 megawatt North Anna nuclear power station declared an alert after losing electricity from the grid but its safety systems kicked it and it was now operating normally, officials said.
The US Geological Survey said the epicenter was 38 miles (61 kilometers) from Richmond, Virginia, and 84 miles (135 kilometers) from Washington.
It was the largest quake in Virginia since May 1897, when a 5.9 quake struck near the state's western edge.
The Pentagon, the world's biggest office building located across the River Potomac from the capital, ordered a brief evacuation, which was carried out calmly.
Several hundred people streamed out of the building and officials said there was no damage other than a ruptured water line.
