Authorities in the United States have warned residents to stay indoors after a fierce winter storm killed at least 11 people, with forecasters saying on Saturday that the Arctic blast could hit record lows.
A state of emergency was declared in New York and New Jersey after heavy snow fell on Thursday and there was no sign of respite from the brutal chill that has struck since the start of the year in parts of the northeast U.S. and Canada.
One of the coldest Arctic outbreaks in the past two decades is now set to plunge the Midwest close to record lows, weather forecasters say, predicting Chicago could see some of its coldest weather ever on Monday, with temperatures hovering around minus 10 degrees Fahrenheit (minus 23 degrees Celsius).
Gusty winds could bring what forecasters at the National Weather Center called "very dangerous levels" of wind chill.
"Incredibly, it may feel as cold as -50 to -60 (Fahrenheit) on Sunday night over sections of the north-central states with the frigid air remaining in place into early next week," it said.
Authorities have urged people in the worst-hit areas to spend the first weekend of the new year indoors for their own safety and to allow rescue and clean-up teams to get to work as quickly as possible.
"Chicagoans are a hearty bunch," said Matt Smith, spokesman for the Chicago Department of Family and Support Services.
"But when temperatures get as cold as they are predicted, you want to start thinking out things in advance," the Chicago Tribune quoted him as saying, adding that the department had advised people stay indoors and to stock up on medical supplies and food.
De Blasio shoveled snow in front of his Brooklyn house on Friday before repeating appeals for drivers to stay off the roads to help the city clear its 6,200 miles (9,900 kilometers) of roads.