People crowd Pennsylvania Avenue in Washington on Tuesday as they evacuate buildings after an 5.8-magnitude earthquake hit the area. Charles Dharapak / Associated Press

WASHINGTON - When people in the US capital realized that a rare earthquake had just hit the area at 1:51 pm on Tuesday, they felt some kind of relief.

Only three weeks before the 10th anniversary of the attacks on the United States on Sept 11, 2001, the city was preparing for something worse.

So far, there have been no reports of deaths, serious injuries or damage.

Residents were told to remain alert and prepare for possible aftershocks.

"Today's earthquake in the mid-Atlantic region is a great reminder that emergencies can strike anywhere and often happen without warning," the White House blog said.

It also suggested that people have an emergency plan and a kit of emergency supplies to sustain themselves for at least 72 hours.

The 5.8-magnitude quake was the strongest on the US east coast since 1944.

The epicenter in Mineral, Virginia, located 135 km southwest of Washington DC, was 6.4 kilometers deep, according to the US Geological Survey.

Millions of people from Georgia to Canada felt the quake.

As people in the area are unaccustomed to earthquakes, most were confused when the ground began shaking, thinking it may have been an explosion, a crash or a bombing.

"I was at a lunch meeting on Connecticut Avenue when the quake happened," Chu Yibin, a non-governmental organization employee, told China Daily.

"We felt a strong trembling for a few seconds but thought it might just be a bus passing by."

Hundreds of workers in the downtown area spilled out from the office buildings several minutes after the quake.

Phone services were disrupted throughout the region as network congestion prevented cell phone users from making calls.

"I was sitting in the conference room on the 10th floor (when the quake struck)," said Xu Ting, an employee of a Washington-based think tank.

"Then I felt some dust falling from the ceiling and saw the glass walls swaying."

Xu used to live in Japan, so she was more familiar with the signs of an earthquake. "But an earthquake in DC? It's so weird," she said.

The Pentagon was evacuated first, and the White House, US Capitol, and other federal buildings were also evacuated soon afterward.

The quake made chandeliers sway in the Capitol and the floor of the US Senate shook before staff headed for the exits. Some minor damage could be seen in the rotunda, under the dome of the Capitol.

Chunks of plaster fell from above a doorway in the Capitol's Statuary Hall. The US Congress is in recess, so most members were away.

"I thought at first somebody was shaking my chair, and then I thought maybe it was a bomb," said Senate aide Wendy Oscarson-Kirchner.

All national monuments and parks in Washington were "stable but closed" following Tuesday's earthquake, US Park Police spokesman Sergeant David Schlosser said.

Two nuclear reactors at the North Anna Power Station near the epicenter were automatically taken off line by safety systems, according the Associated Press.

Reuters contributed to this story.