(CNN) -- At least two confirmed tornadoes descended upon towns in western Massachusetts on Wednesday, leaving at least four dead and smashing homes and buildings across a 40-mile stretch, state officials and witnesses reported.

One person was killed in Springfield, two in nearby Westfield and one in Brimfield, about 20 miles east, Massachusetts Gov. Deval Patrick told reporters Wednesday night.

The storms struck shortly after 4 p.m. in Springfield, about 90 miles west of Boston. Dylan McDonald told CNN he watched the tornado knock down trees and scatter debris across town as he was driving with a co-worker.

"As the light turned green, a tree fell and everything took off," McDonald said. "We saw a roof fly off an apartment building. The car was tilting, but didn't turn over."

As many as 19 communities reported tornado damage Wednesday evening, Patrick said. The governor declared a state of emergency as the storm system that spawned those twisters moved east, with watches posted all the way to the Atlantic coast until late Wednesday.

"It's been particularly devastating in downtown Springfield," Patrick said. And he said a local official told him, "You have to see Monson to believe it."

Monson resident Dolly Opper said state police were setting up roadblocks around the town, and a neighbor described the town's center as "war zone."

"I haven't been home," she said. "The steeple's off the church across the street. It's lying right in the front yard."

At J.T.'s Sports Pub, on Springfield's Main Street, owner Keith Makarowski said he and the 10 or so patrons intially went outside to watch the darkening skies -- then retreated as the storm blew into downtown.

"There was a ton of debris flying around, lots of roof shingles and random siding," Makarowski said. Several century-old buildings were damaged -- "roofs torn off, facades ravaged, trees uprooted" -- and a woman across the street was blown up against a building after being caught outside.

"Luckily, two people from inside the building were able to pull her in, and she seemed like she was OK," Makarowski said.

Massachusetts State Police Sgt. Michael Popovics said Springfield, Monson, Westfield and seven other towns -- Agawam, Charlton, Oxford, Palmer, Sturbridge, West Springfield and Wilbraham -- reported severe damage. Sandra Ahearn, a spokeswoman for the Western Massachusetts Electric Co., said 12,000 customers were without power in the utility's service area and that hard-hit areas might not have electricity until the end of the week.

Patrick said he has mobilized 1,000 National Guard troops to assist with cleanup and search-and-rescue operations. The Massachusetts State Police said it had activated dog teams to look for people in damaged buildings and described many streets in Springfield as "impassable" due to fallen power lines and trees.

The damage came amid a wave of heavy thunderstorms that moved through the Northeast on Wednesday afternoon. Tornado watches were also issued for northern Connecticut, Rhode Island, New Hampshire and Maine until 11 p.m. Wednesday.

Though not as tornado-prone as much of the Midwest or South, Massachusetts has averaged two to three twisters per year since 1950, according to figures from the National Oceanic and Atmospheric Administration. In 1953, a massive tornado that struck Worcester and nearby towns killed 90 people, according to NOAA; the last tornado to hit the state was in 2008.

CNN's Jennifer Westhoven, Anna Gonzalez, Matt Smith, Leigh Remizowski, Julia Talanova and Sean Morris contributed to this report.