A magnitude 5.9 earthquake has shaken the east coast of the United States and Canada from Virginia to Toronto.
The tremor shook buildings, and a number in Washington and New York were evacuated, but there are no immediate reports of major damage or injuries.
The US Geological Survey said the epicentre of the quake was near the town of Mineral in Virginia.
It struck shortly before 7pm Irish time.
Control towers at JFK International Airport in New York City and Newark Liberty Airport in New Jersey were also evacuated, and flights were grounded briefly in Washington, Philadelphia and New York.
The quake was felt as far away as Toronto. Buildings in Boston were evacuated, and some people who experienced swaying offices said they felt their stomachs turn.
The Pentagon, the US Capitol and monuments in Washington were all evacuated after the shallow quake.
The disruption to mobile phone services in the hour after the quake added to the sense of fear in a country preparing to mark the 10th anniversary of the 11 September 2001 terror attacks.
There were no immediate reports of injuries, but the tremor also hit as emergency officials warned of a possible strike on the east coast of Hurricane Irene, which was roaring through the Atlantic Ocean.
Seismologists said the epicentre was 47km from Charlottesville, Virginia, and 139km from Washington, where Reagan National Airport also ordered some evacuations.
In Washington, a national park helicopter was seen circling the Washington Monument, inspecting the landmark for cracks.
Only minor damage was reported in Washington as the quake shook plaster from walls and, according to a CNN report, knocked damaged pinnacles from the National Cathedral.
The cathedral said on its website that it was closed pending an investigation of damage.
The US Geological Survey said the earthquake was the largest in the state of Virginia since May 1897, when a 5.9 quake struck in Giles County, near the western edge of the state.
