Deadly tornadoes swept through the heart of western and central Massachusetts, leaving a trail of destruction and killing 4 people even as rescue efforts were hampered by heavy thunderstorm and hail.

The tornadoes, which struck Springfield, the third largest city in Massachusetts with a population of 150,000 people, uprooted trees and buildings on late Wednesday night, and caused extensive damage, prompting Gov. Deval Patrick to declare a state of emergency and mobilize the National Guard.

The tornadoes left at least 50,000 houses without power and in most houses, power is not expected to be restored for a week.

Patrick said two people died in Westfield, one in West Springfield and one in Brimfield. Tornadoes were also reported in several other communities, including Monson and Sturbridge.

Springfield Mayor Domenic J. Sarno said at least 40 people were injured and efforts are going on to rescue people who are trapped under debris.

Firefighters and police crews are going from house to house to assess the damage the tornadoes have caused and rescue trapped victims, Sarno said.

However, rescue efforts have become difficult because of weather-related problem and power outage.

A firefighter said the true extent of damage will not be known until daybreak.

A witness called the scene a war zone. He said the first tornado struck during rush hour and a second one struck at about 6:20 p.m. The tornadoes were accompanied by heavy winds, hail and thunderstorm.

This is the most deadly tornado Massachusetts has faced since May 29, 1995, when a tornado killed three people in the town of Great Barrington.

Tornado alerts have been sounded for most of the East Coast, including Philadelphia, New York and Boston.

Special watch has been sounded for northern Connecticut, Rhode Island, New Hampshire and Maine.

Weather experts say this is the deadliest tornado season in decades. In April, southern states faced the wrath of twisters and last month, a massive twister killed 134 people in Joplin, Missouri.

Watch the tornado weave a path of destruction in Springfield: