This post has been updated.

Virginia Robert F. McDonnell (R) said Tuesday afternoon that the state is working with federal, state and local agencies to assess damage from the earthquake.

"In the wake of the earthquake, I would like to encourage all Virginians to check on neighbors and loved ones to ensure that everyone is safe and to continue cooperating with law enforcement and emergency responders working in your neighborhood,’’ said McDonnell, who is holding a news conference later today. “All resources of the commonwealth have been put on alert to assist in any way necessary as we move forward.” 

Buildings on Capital Square, including the Patrick Henry Building that houses McDonnell’s office, were evacuated after downtown Richmond felt shaking for 20 seconds.

Dominion Resources has shut down both reactors at the North Anna nuclear power plant, though no damage has been reported. 

The emergency diesel generators started as off-site power from the grid was lost. The station declared an alert, the next to the lowest of the four emergency classifications of the U.S. Nuclear Regulatory Commission.

The earthquake also caused the company’s newest power station, Bear Garden in Buckingham County, to shut down automatically. The earthquake was felt at the Surry Power Station, but not as strong. Both units continue to operate, according to Dominion.

U.S. nuclear power stations, including Dominion’s four stations, were built to seismic standards for their regions and safety systems designed to those standards would direct operators to shut down the reactors in the event of an earthquake, according to Dominion.

UPDATE: 5:45 p.m

McDonnell said at a late afternoon news conference in Richmond that Tuesday's earthquake was the largest to hit Virginia since 1897. 

He said the earthquake hit at 1:51 p.m. four miles south of Mineral in Louisa County, 41 miles northwest of Richmond, and was felt as far away as Rhode Island. 

The governor was in his Capitol Square office speaking to his son, who attends the University of Virginia, when both of them felt the tremor.

He said no deaths or significant damage have been reported, but that state and local officials are still evaluating property.

"The very good news is any injuries have been very minor,'' he said. 

Both Louisa middle and high schools sustained some damage. Louisa elementary school will be used as a shelter Tuesday night, if needed.

 The state's emergency operations center already was intact in preparation for Hurricane Irene, which is supposed to hit the Atlantic Coast this weekend.

In the 50 Virginia jurisdictions holding primaries, voting will proceed as scheduled. McDonnell said that a small number of precincts had moved voting outside as a result of the earthquake.

McDonnell, who said he did not have the legal authority to extend voting hours, said he saw no reason to cancel or postpone the voting since no polling machine had more than a 30-minute delay. “We don’t believe any voter has been deprived of their vote,” he said.