A worker clears ice-covered branches from a closed road in New Hampshire. (Charles Krupa/Associated Press)Some people in New Hampshire who had their electricity knocked out by an ice storm may have to wait until the end of the work week before power is restored, a state official said Sunday.

"This is a real slow-going, labour-intensive kind of operation," said Jim Van Dongen of the department of emergency management. "There's not going to be any quick fix. It's going to be a line at a time, a mile of line at a time."

Roughly 649,000 homes and businesses were still without power Sunday morning in upstate New York, Massachusetts, New Hampshire, Vermont and Maine. More than a third of those customers were in New Hampshire.

Utility officials have warned there could be more outages as drooping branches shed ice and snap back to their original positions, potentially taking out more power lines.

"We're looking at a little milder weather. Tomorrow, it's going to get perhaps as high as the 50s (10 C), so a lot of that stuff is going to come falling out of the trees," Van Dongen told CBC News.

About 1.25 million customers were without power at the peak of the storm's aftermath on Friday.

"People have gone to hotels. They've gone to neighbours in areas where there is power. A lot of people are toughing it out with wood stoves or using generators, and of course, we're a little bit concerned about that," Van Dongen said.

He reported "a number of cases" of carbon monoxide poisoning involving people trying to heat their homes. At least four deaths appear to be related to the storm.

A couple in their 60s died in Glenville, N.Y., when a gas-powered generator running in an attached garage filled their house with carbon monoxide, police said Saturday.

The body of a Marlborough, Mass., public works supervisor was recovered from a reservoir Saturday afternoon, a day after he went missing while responding to tree limbs down.

And in Danville, N.H., authorities said a man died of carbon monoxide poisoning after he failed to properly vent a gas-powered generator inside his camper.