Earthquake closes Washington Monument indefinitely (VIDEO)

The Washington Monument will be closed indefinitely to the public in the wake of Tuesday's 5.8-magnitude earthquake, with National Park Service engineers finding a crack near the top of the 555-foot landmark on the National Mall.

Structural engineers warned that the full effect of the earthquake — the most powerful to strike the East Coast in 67 years, according to the AP — might not be known for days, the Washington Post reports.

The quake centered on the state of Virginia but was felt in Washington, where the Pentagon and Capitol were evacuated, the AP reports, as well as in New York, and reportedly as far afield as Georgia and Toronto.

(GlobalPost reports: Earthquake shakes U.S. east coast; Pentagon evacuated)

Park service spokesman Bill Line said Tuesday night that structural engineers found the crack where the Washington Monument — both the world's tallest stone structure and the world's tallest obelisk — narrows considerably, the LA Times reports.

The monument will remain closed "until further notice," the NPS website reportedly said.

The newly opened Martin Luther King, Jr. Memorial, Franklin Delano Roosevelt Memorial, the World War II Memorial, Vietnam Memorial and the Korean War Memorial remain open, however.

(GlobalPost reports: Washington glimpses Martin Luther King memorial — made in China)

Tuesday's quake was made more alarming by the approaching 10th anniversary of the Sept. 11, 2001 terrorist attacks, the AP reports, with people "shaken physically and emotionally and poured from high-rises like the Empire State Building in New York, sick with mental images of planes and bombs."

"I ran down all 60 flights," accounting office worker Caitlin Trupiano said. "I wasn't waiting for the elevator."