The U.S. Geological Survey reported a 3.6 magnitude earthquake centered in Montgomery County at 5:04 a.m. Friday.

The epicenter was in Gaithersburg near the intersection of Forest Brook and Waring Station roads (39.145°N, 77.222°W), USGS reported in a preliminary finding. Its depth was 3.1 miles.

Authorities in the District and Montgomery and Arlington counties said there were no reports of damage.

“We are getting flooded with calls,” a Montgomery County police spokesperson said.

Amy Vaughan, a spokesperson for USGS, said the quake was the largest recorded within about 30 miles of Washington since a database was created to track such activity in 1974. Previously, the largest earthquake reported during that time period was a 2.6 magnitude tremor in 1990.

"So this is pretty significant for your area," Vaughan said in a telephone interview with WRC-TV (Channel 4).

At the same time, she said, earthquakes are possible anywhere, because of the continual seismic activity under the Earth's crust. "It may be rare and unexpected, but not unheard of," Vaughan said.

Vaughan said USGS was receiving reports from as far away as Pennsylvania from people who had felt the quake. Given the relatively low magnitude of the tremor, she said, it was not likely it caused any significant structural damage.

"It's going to be very widely felt, more than damaging, we suspect," Vaughan said.

Jahi Chikwendiu, a Washington Post photographer, said he heard and felt the tremor at his home in Reston while he was standing in the kitchen. It was strong enough to wake his wife, who was sleeping upstairs, Chikwendiu said.

"I thought it was thunder at first," he said.

Dean Miletich, of Frederick, said he was taking out the trash when the quake hit.

“When I came back into the garage, everything on the shelves were shaking,” he said. “It sounded like a deep rumble. When I came back inside, my wife had woken up and asked me, 'What did you do?'”