HARTFORD, Conn. — Residents across the Northeast faced the prospect of days without electricity or heat Monday after an early-season storm dumped as much as 30 inches of wet, heavy snow that snapped trees and power lines, closed hundreds of schools, and disrupted plans for Halloween trick-or-treating.

Communities from Maryland to Maine that suffered through a tough winter last year followed by a series of floods and storms went into now-familiar emergency mode as roads closed, shelters opened and regional transit was suspended or delayed.

The storm’s lingering effects, including power failures and hundreds of closed schools, will probably outlast the snow. Temperatures are expected to begin rising Monday and the snow will start melting, the National Weather Service said.

The early nor’easter had utility companies struggling to restore electricity to more than 3 million homes and businesses. By midday Monday, the number without power was still above 2 million but falling. But officials in some states warned it could be days or even a week before residents have power again.

In Allentown, Pa., tree branches littered yards and residents girded for a long haul without power. Anne Warschauer, a 91-year-old Holocaust survivor from Germany, refused to leave her home on a quiet tree-lined street even though the temperature inside had plummeted.

“I’m freezing,” she acknowledged. But she said she worried about her cat, Pumpkin.

“They’re not going to get the power back on until Thursday, Anne. You can’t stay here,” said her friend, 63-year-old Emma Saylor.

“I’m not going,” Warschauer replied. “So let’s not talk about that anymore.”

The trees, branches and power lines crisscrossing roads and rail lines led to a tough Monday morning commute for many. Motorists hunted for open gas stations as power failures rendered pumps inoperable; at a 7-Eleven in Hartford, two dozen cars waited in a line that stretched into the street and disrupted traffic.

“There’s no gas anywhere,” said Debra Palmisano, of Plainville, who spent most of the morning looking around the capital city. “It’s like we’re in a war zone. It’s pretty scary, actually.”

Some local officials canceled or postponed Halloween activities, fearful that young trick-or-treaters could wander into areas with downed power lines or trees ready to topple.

The snowstorm smashed record totals for October and worsened as it moved north. Communities in western Massachusetts were among the hardest hit. Snowfall totals topped 27 inches in Plainfield, and nearby Windsor got 26 inches.

In New Hampshire’s capital of Concord, more than 22 inches fell, weeks ahead of the usual first measurable snowfall. States of emergency were declared in Connecticut, Massachusetts, New Jersey and parts of New York.

West Milford, N.J., had 19 inches Sunday. Gov. Chris Christie declared statewide damage to utilities worse than that wrought by Hurricane Irene, a deadly storm that blew through the state in August.

Things were similar in Connecticut, where the power loss of 800,000 broke a record set by Irene. By early Monday, around 400,000 people lacked power in New Jersey and more than 750,000 in Connecticut.

Compounding the storm’s impact were unfallen leaves that gave the snow something extra to cling to and loaded branches with tremendous weight, snapping them off and sending them plunging onto power lines and across roads and homes.

Along the coast and in such cities as Boston, the relatively warm ocean helped keep snowfall totals lower. Washington received a trace, tying a 1925 record for the date.

New York City’s Central Park set a record for both the date and for October with 1.3 inches — not much by normal standards but enough to damage an estimated 1,000 trees. Caretakers raced to clean up before the New York City Marathon, which goes through the park and is only six days away.

The snowstorm was blamed for at least 12 deaths, mostly caused by falling trees, traffic accidents or electrocutions. Six people died in Pennsylvania alone.

Amtrak had suspended service on several routes, and one train from Chicago to Boston got stuck overnight in Palmer, Mass. The 48 passengers had food and heat, a spokeswoman said, and were taken by bus Sunday to their destinations. Delays persisted into Monday on some of Amtrak’s New England routes.

North of New York City, dozens of motorists were rescued by state troopers after spending 10 hours or more stranded on snowy highways in Dutchess and Putnam counties. Dimitra Richardson and her son Dana, of Malverne, N.Y., were among them.

“It couldn’t be helped; nature acts whenever it wants,” said Richardson, an 82-year-old retired literature professor and dean at Adelphi University. “The authorities tried their best, but it seems like they were totally unprepared.”

Passengers on at least three JetBlue planes and one American Airline plane said they were stranded on the tarmac for seven hours or more after being diverted from New York-area airports on Saturday.

Crews worked to raise a barge that sank during the storm in Rhode Island’s Narragansett Bay that contained 2,400 gallons of diesel fuel. Officials said a minor sheen was visible on the water.

The storm sank many Halloween festivities, too.

In the New York village that was the setting of Washington Irving’s Gothic tale “The Legend of Sleepy Hollow,” the town’s annual Haunted Hayride was called off because of broken limbs and dangling branches.

Sharon Martovich of Southbury, Conn., who was grocery shopping Sunday morning in nearby Newtown at one of the few businesses open for miles, said she hoped the power would come back on in time for her husband’s Halloween tradition of playing “Young Frankenstein” on a giant screen in front of their house.

“We would be really sad and it would disappoint a lot of people if we can’t play ‘Young Frankenstein,'” she said. But no matter what, they will make sure the eight or so children who live in the neighborhood don’t miss out on trick-or-treating.

“Either way we will get the giant flashlights and we will go,” she said.

Many Northeasterners were trying to take the storm in stride after a string of two harsh winters — many communities set or approached snowfall records last winter — followed by flooding from tropical systems Irene and Lee.

Doug Burdi, a scientist from Arlington, Mass., northwest of Boston, had the day off Monday because the pharmaceutical company he works for lost power. Burdi said he’s not yet ready to worry about another harsh winter, despite the intensity of the early storm.

“Let’s call it a freak. It makes us feel better when we think of it that way,” he said. “I don’t want to be fatalistic about it.”

The National Weather Service acknowledged that residents shouldn’t necessarily expect “Snowtober” a harbinger of a hard winter to come. Long-term models indicate a slightly drier start to the season, although there’s a chance of above-normal precipitation later on, said Aaron Tyburski, a meteorologist in State College, Pa.

“There’s always going to be anomalous events,” he said. “While it is quite an event, we may go the next month and not get any snow.”