The U.S. Geological Survey at first estimated 7:12 p.m. quake as a 4.6 magnitude, but later downgraded that to 4.0. The epicenter, about 3 miles west of Hollis Center, Maine, is about 3 miles deep. That location is about 20 miles west of Portland. The Maine Emergency Management Agency had no immediate reports of damage or injuries.

About 10 miles away in Waterboro, about 20 customers and staff at Waterboro House of Pizza ran outside when they heard a loud bang and the building shook.

"It was loudest bang you ever heard in your life. We actually thought it was an explosion of some type," said owner Jessica Hill. "The back door and door to the basement blew open."

In nearby Saco, Sue Hadiaris said, "The whole house shook. It felt like a train was coming right through the house. It was very unnerving because you could feel the floor shaking. There was a queasy feeling."

Afterward, Hadiaris called her 15-year-old niece in Falmouth to make sure she was safe. "She said, 'We can cross that off our bucket list. We've lived through an earthquake,"' Hadiaris said.

Lynette Miller, a Maine Emergency Management Agency spokeswoman, said her dogs started barking several seconds before the quake. "It was several seconds of good shaking but nothing falling down," Miller said from her home in Readfield, about 60 miles north of Portland. The Seabrook Station nuclear plant, about 63 miles away in New Hampshire, declared an unusual event - the lowest of four emergency classifications, but said it was not affected. The plant has been offline for refueling.

"There has been no impact at all to the plant from the earthquake and our refueling maintenance activities have not been affected," said Alan Griffith, spokesman for Next EnergyEra Seabrook Station.