An earthquake in central Virginia was felt across much of the East Coast on Tuesday, causing light damage and forcing hundreds of thousands of people to evacuate buildings in New York, Washington and other cities.
No tsunami warning was issued, but air and train traffic was disrupted across the Northeast and mid-Atlantic.
In the Washington area, parts of the Pentagon, White House and Capitol were among the areas evacuated for several hours. All memorials and monuments on the National Mall were evacuated and closed for inspections.
Around 7:30 p.m. EST, the National Park Service reopened the Lincoln and Jefferson Memorials to the public, but officials decided to keep the Washington Monument closed. After a secondary inspection, NPS officials discovered some cracking in the stones near the top of the monument. Structural engineers will be brought in to evaluate the cracks.
Park service spokesman Bill Line said Tuesday night that structural engineers found the crack where the 555-foot landmark narrows considerably.
He says the lower portions checked out fine earlier but later they found the crack. He says the monument will be closed indefinitely to keep the public safe.
An outside engineering service will study the crack on Wednesday. He says it's too early to say what would be involved in fixing it.
The 91,000-ton monument is made of Maryland marble.
At the Pentagon, a low rumbling built and built to the point that the building shook. People ran into the corridors of the government's biggest building and as the shaking continued there were shouts of "Evacuate! Evacuate!"
NBC Pentagon corresponent Jim Miklaszewski said the rumbling was eerily similar to the impact on Sept. 11, 2001, when al-Qaida terrorists flew a jetliner into the Pentagon. "I, like many other people here, thought 'Oh my God, we've been hit again.'"
The quake ruptured a water pipe inside the Pentagon, flooding parts of two floors.
Initial damage reports from Washington included plaster falling off the Capitol building and three pinnacles falling off the 30-story-tall central tower at the National Cathedral.
There were no reports of deaths or serious injuries.
Centered some 90 miles south of the nation's capital, the quake was a magnitude 5.8, the U.S. Geological Survey said Tuesday after an earlier estimate of 5.9.
The quake was tied for third strongest along the East Coast in recorded history, USGS records show. Charleston, S.C., was hit by a 7.3 in 1886 and Giles County, Va., saw a 5.9 in 1897. A 5.8 quake struck New York state in 1944.
Several hours after the first earthquake, a 4.2 magnitude aftershock hit in Mineral, Va., just after 8 p.m., EST, according to USGS. Mineral is around 35 miles northwest of Richmond. NBC News' Tom Costello reported that a low rumble was heard as the aftershock occurred.
Two nuclear reactors near the epicenter were taken offline as a precaution, officials said. No damage was reported at either.
Dominion Resources Inc said its 1,806-megawatt North Anna nuclear station in Virginia was designed to withstand a 6.2 magnitude earthquake, a spokesman told Reuters.
At the U.S. Capitol, light fixtures swung and the building shook for about 15 seconds while the tremor hit, NBC News reported.
"I thought at first somebody was shaking my chair and then I thought maybe it was a bomb," said Senate aide Wendy Oscarson-Kirchner.
At Reagan National Airport outside Washington, ceiling tiles fell during a few seconds of shaking. All flights were put on hold and one terminal was evacuated due to a gas smell.
In New York City, NBC reported debris fell from the attorney general's office, causing a brief panic as people ran from the area.
Airport towers and government buildings in New York, including City Hall, were evacuated. The 26-story federal courthouse in lower Manhattan began swaying and hundreds of people were seen leaving the building.
Flights from the New York area's John F. Kennedy and Newark airports were delayed while authorities inspected control towers and runways. Philadelphia's airport also halted flights for inspections.
New York Mayor Michael Bloomberg reported "no reports of significant damage or injuries in New York City at this time."
A mild tremor was even felt by NBC reporters with President Barack Obama during his vacation on Martha's Vineyard, an island off Massachusetts.
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, 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, Md., the quake sent office workers into the streets, where lamp posts swayed slightly as they called family and friends to check in.
Amtrak reported train service along the Northeast Corridor between Baltimore and Washington, was operating at reduced speeds as crews inspected the lines.
The earthquake’s epicenter was near Mineral, Va., the USGS reported. It struck at 1:51 p.m. ET.
In Mineral, the roof of the town hall collapsed in the quake.
East Coast earthquakes are far less common than in the West, but they tend to be felt over a broad area. That's 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 USGS seismologist Susan Hough.
At NBC's Washington bureau, it took a few seconds for staffers to realize what was going on, with people asking one another if it was an earthquake.
No alarms sounded but people then began rushing out, congregating in front of the building as they would for a fire drill.
Outside the building, people tried making calls, but no one could get service.
Next door, staffers for the Department of Homeland Security evacuated their building.
"I was probably in three earthquakes in Los Angeles," said NBC news producer Mark Miano, "and this was by far the strongest I’ve ever felt."
The D.C. area last felt an earthquake on July 16, 2010, when a 3.6 magnitude quake struck.
The USGS said the quake was not related to one in Colorado on Monday.