By Ros Krasny
BOSTON (Reuters) - A moderate earthquake struck the northeastern U.S. state of Maine on Tuesday shortly after 7 p.m. (2300 GMT), according to the U.S. Geological Survey.
First reported as a 4.5 magnitude quake centered near Lake Arrowhead, the USGS revised the quake's magnitude to 4.6 and finally down to 4.0.
It shifted the epicenter to close to Hollis Center, southeast of the original location, and revised the quake's depth from a deep 17 miles to a relatively shallow 3 miles.
Hollis Center is about 20 miles west of Portland, Maine's most populous city, and about 100 miles north of Boston.
Eyewitnesses across the Boston area reported feeling the quake for up to 20 to 30 seconds.
The quake was felt in much of New England, including much of Vermont, New Hampshire, Rhode Island and Connecticut. A few reports were also received from upstate New York, the USGS said.
A spokeswoman for the Maine State Police in the Portland area said there were no immediate reports of damage or injuries.
Massachusetts Governor Deval Patrick said state emergency personnel were monitoring the situation but also had no reports of damage.
Quakes are not unknown in the region, which has felt "small earthquakes and suffered damage from infrequent larger ones since colonial times," the USGS said on its website.
(Reporting By Ros Krasny and Tim McLaughlin; Editing by Eric Beech)