The coldest wind chill ever in the continental United States was recorded on Friday due to an "epic, generational" Arctic cold snap, forecasters said.
Arctic blasts drove the wind chill on Mount Washington on Friday evening to a new record low of -78C, according to the US National Weather Service.
That broke the previous low recorded there of -74C, the Weather Channel said.
At almost 6,300 feet, Mount Washington is the highest peak in northeast America and it is known for having some of the world's worst weather.
The Arctic wind blew into the United States from eastern Canada on Friday morning, causing temperatures to plunge to dangerously low levels across the region.
Wind-chill warnings were issued for most of New York state and across all six New England states - Massachusetts, Connecticut, Rhode Island, New Hampshire, Vermont and Maine - a region home to about 16 million people.
The brutal temperatures and high winds were blamed for the death of a child in Southwick, Massachusetts, after a tree fell onto a vehicle.
The driver was taken to the hospital with serious injuries, but the infant died, authorities said.
Extreme weather warnings covering several million people were in effect across much of New England, Quebec and eastern Canada.
"This is an epic, generational arctic outbreak," the national weather service in Caribou, Maine, warned in an advisory ahead of the front.
Hypothermia and frostbite
In New York City, a "code blue" regulation was in effect, meaning no homeless shelter could turn anyone away.
On Friday, schools shut in Boston and Worcester, Massachusetts, New England's two largest cities, amid concerns over the risk of hypothermia and frostbite for children walking to school or waiting for buses.
Michelle Wu, the Boston mayor, declared a state of emergency through Sunday and opened warming centres to help the city's 650,000-plus residents cope.
Meanwhile, a Pacific storm was expected to bring another round of heavy snow to California's Sierra Nevada mountains on Saturday night.