Massachusetts officials went door-to-door Thursday morning looking for people who may be trapped in damaged buildings after tornadoes swept through more than 20 communities, killing at least four people.

In a state where twisters are an unusual if not rare occurrence, two tornadoes touched down in central and western parts of the state Wednesday, including one in Springfield, the state's third-largest city. More than 20 communities reported possible tornadoes touching down, said Scott MacLeod, spokesman for the Massachusetts Emergency Management Agency.

Gov. Deval Patrick told ABC's "Good Morning America" on Thursday that considering how quickly the tornadoes formed, he feels fortunate there weren't more fatalities.

"When I spoke with the mayor of Springfield yesterday, he told me they had about ten minutes' warning," Patrick said. "When you consider how quickly the tornadoes developed and then touched down, the fact that there wasn't even greater damage and loss of life is a remarkable thing."

Sens. John Kerry and Scott Brown joined Patrick on a helicopter tour of the damaged areas, including Springfield. Kerry said it looked like a "blast zone" and was confident that federal disaster aid would be made available, particularly because of damage to businesses.

Patrick said it was unbelievable that so much destruction was caused in such a short period of time.

"We have a real mess on our hands," he said. "People are badly shaken. There are folks who have lost everything."

Experts planned to assess damage by air and land Thursday to determine the number and strength of the tornadoes, National Weather Service meteorologist Benjamin Sipprell said.

Patrick declared a state of emergency and activated 1,000 National Guard troops.

More than 55,000 homes were left without power as toppled trees knocked out electric lines.

The storm splintered and sheared roofs along Main Street in Springfield, a city of more than 150,000. A mounted video camera captured dramatic scenes of a debris-filled funnel as it moved in from the west.

"For us here in Massachusetts, it's a bit unusual" to have tornadoes, MacLeod said. "On an annual basis we might see one, two or three tornado watches a year. … The impact is more significant than we have seen in many, many years."

Two deaths were in Westfield, one in West Springfield and one in Brimfield, the spokesman said. State police said at least 33 people were injured in Springfield, five of them seriously.

"It's been particularly devastating in downtown Springfield and the communities of Springfield and Monson," the governor said at a news conference.

Until killer tornadoes struck Alabama and Missouri last month, leaving hundreds dead, the nation's deadliest tornado was the one that struck Worcester, Mass., in 1953, killing 94 people, the state emergency agency said.

Weather Channel senior meteorologist Matt Crowther said Massachusetts does see some tornadoes but usually in summer when temperatures are at their peak. Wednesday's twisters were triggered by unusually humid and warm conditions combined with wind shears, in which surface winds and winds aloft are moving in different directions, Crowther said.

"It's a little unusual for this time of year," he said.

Patrick asked superintendents in affected communities to cancel school today to aid in the cleanup.