BOSTON – Thousands of people across the Northeast had no electricity for alarm clocks and air conditioners Monday after waves of violent thunderstorms.

Wind gusting to 80 mph knocked trees onto power lines, lightning started fires, and torrential rain flooded streets in parts of eastern Pennsylvania, northern New Jersey, southeastern New York, Connecticut and eastern Massachusetts on Sunday.

“It’s really testing our crews. It’s pretty extensive,” Connecticut Light & Power spokesman Mitch Gross said of the damage late Sunday.

Boston’s South Shore was hit particularly hard, with severe flooding in Quincy, Braintree, Weymouth and Brockton.

“Half of the city is underwater,” Brockton police dispatcher Darrelyn Jordan said Sunday night. “We have reports of water going into basements all over the city. We’ve had people stuck in cars all over the city. We even had to tow a police cruiser out of there with water flowing over the hood.”

The mayor of Stamford, Conn., said the damage was the worst since an ice storm in 1973. “We’ve never seen anything like it,” said Dannel Malloy.

More than 50,000 homes and businesses in Massachusetts and more than 80,000 in New Jersey lost power, though most had service restored by Monday morning.