US: In New York you have to guard against traffic, hustlers, falling masonry - and yesterday, frostbite, writes Conor O'Clery North America Editor
Early in the morning the temperature plunged to 1 degree Fahrenheit (-17C), matching the record set in 1893, according to the National Weather Service.
With a stiff wind making it feel twice as cold, New Yorkers were warned of the danger of frostbite.
"Any exposed skin can freeze in less than 30 minutes," forecaster Scott Reynolds said.
At least seven people have died in the cold snap in the north-east of the US, including a hiker found in the White Mountains of New Hampshire.
The cold air came straight from the North Pole across the frozen Hudson Bay with no catalyst to moderate the temperatures, said meteorologist Tim Markle, at the Mount Washington Observatory in New Hampshire, where the temperature fell to minus 45 Fahrenheit and the wind chill approached minus 100.
In snow-covered New York police scoured the streets for homeless people to bring them inside, even against their will. Ferries on the Hudson had to make their way through ice.
In Boston the harbour froze, and ice-breakers were used to clear the way for shipping.
Some areas closed schools, fearing that if children missed the bus they would suffer hypothermia within minutes.