More than 70,000 customers were without electricity in the north-eastern US on Saturday, a major sign of a powerful storm known as a nor’easter that was expected to create dangerous conditions through the weekend.

Forecasters warned of gale winds that could down trees and heavy inundations that could flood roads.

Tens of millions of people are in the path of the storm that is already beginning to lash the region with strong winds and rain as the region braces for much more. Dangerous flooding is expected along the mid-Atlantic coast, particularly near New Jersey and Delaware, according to the National Weather Service (NWS).

In the coastal New Jersey borough of Surf City, water, with waves rippling along its surface, flooded the streets, inundating some homes. About 34 miles (55km) up the coast in the borough of Manasquan, where some roads were also flooding, the mayor, Mike Mangan, said he expected “a lot of water in the streets for a long time”. A voluntary evacuation had been issued earlier in some low-lying areas of the community.

Concerts were canceled, along with dozens of flights going into airports in Boston, Nantucket and Martha’s Vineyard in Massachusetts on Friday and Saturday. Several airlines were offering to waive some change or cancellation fees for some east coast flights through the weekend.

Brian Kelly, the mayor of the tiny New Jersey beach community of Sea Bright, said the borough was bracing for winds up to 50mph (80km/h) and flooding that could reach up to 6ft (1.8 meters) on some streets. Officials expect the flooding to start on Saturday and worsen by midday.

“It’s going to be worse than average. We do have probably one or two flooding events a year, sometimes more, sometimes less, but I think this one will be closer to an Irene-scale flooding event,” Kelly said, referencing the 2011 storm that caused major flooding in the north-east. “I hope I’m wrong, but that’s my gut feeling.”

Kelly added that he hopes hundreds of residents living in low-lying areas will consider evacuating. He said the town will open its recreation center for evacuees.

Peak wind gusts could approach 60-65mph (97-105km/h) on Cape Cod, Martha’s Vineyard and Nantucket on Friday night and Saturday, and about 50-55mph (80-89km/h) around Boston and 35-40mph (56-64km/h) farther inland, according to Matthew Belk, a meteorologist with the NWS in Norton, Massachusetts.

“It’s definitely going to be a case of the closer to the coast you are, the more impacts from the storm you’re likely to see,” Belk said.

Belk said nor’easters were not unusual as New England moves into fall, but one concern this early in the season was that leaves still remain on trees, creating more wind resistance. That could increase the risk of downed limbs, which in turn could cause power outages and leave debris in roads, he said.

Along the Atlantic coasts of New Jersey and Delaware, wind gusts could reach 60mph (96.6km/h), according to NWS. In south-eastern Connecticut and eastern Long Island, New York, gusts could be almost as powerful, potentially downing tree limbs and power lines.

More than 200 flights to and from airports in Boston, Nantucket, Martha’s Vineyard and New York had been canceled on Friday, and more cancellations were already in place for Saturday.

Meanwhile, the Red Sox announced their weekend series against the Chicago Cubs would be adjusted. The team moved the Sunday-afternoon game to Friday to create a split double-header. Separately, Ed Sheeran announced that his high-profile Friday and Saturday shows at Gillette Stadium in Foxborough, Massachusetts, would be canceled due to the storm.