New Hampshire was the worst affected state in the north-east
Power workers have been struggling to restore electricity to hundreds of thousands of homes in the north-eastern US after Friday's ice storms.
Some roads remained unsafe and schools were closed in several states, despite warmer temperatures.
At least four people are thought to have died as a result of the storm, one of the worst in a decade.
Meanwhile people in parts of the Midwest were advised to stay at home amid blizzards and freezing winds.
North Dakota was the worst affected state in the region, with as much as 13in (33cm) of snow recorded in the town of Williston and roads closed across the region.
Utility companies brought in crews from Virginia, Michigan, and from Canada, to help repair power lines damaged by ice after as many as a million people were left without electricity over the weekend.
Officials said the damage was extensive and much of it could take until Thursday or Friday to repair. In some parts, electrical systems and power lines would need to be completely rebuilt, they said.
The aftermath of the ice storm
More than 400,000 people were still without power on Monday morning, the Associated Press news agency quoted power companies as saying.
Many of them have been forced to stay in shelters, or have checked into motels or hotels.
States of emergency are in force in Massachusetts, New Hampshire and in parts of Maine and New York state.
About 1.4 million homes and businesses across the four states were left without electricity on Friday after a widespread overnight ice storm coated power lines, pylons and trees.
New Hampshire Governor John Lynch and his counterpart in Massachusetts, Deval Patrick, declared full states of emergency and called up members of the National Guard to help.
New Hampshire, the worst-hit of the four states, still had 168,000 homes without power on Monday, AP said.
"We are used to cold, and we are used to snow and ice, but this is a storm that is very unique," Lisa Michaud, executive director of the Greater Manchester Red Cross, told Fox News.
"We received over an inch of ice on top of rain. It came hard and it came fast and we weren't prepared for it."
In New York, Governor David Paterson declared a state of emergency in 16 counties.
The governor of Maine declared a limited state of emergency, enabling utility crews to work longer hours.
A severe ice storm in December last year was blamed for the deaths of at least 22 people in the central US.
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