A winter storm has caused havoc in the northeastern United States as blizzard-like conditions grounded thousands of flights, closed schools and brought dangerously low temperatures.
Up to 13 deaths were being blamed on Friday's storm, which dumped 60cm of snow in some areas.
Governors in New York and New Jersey declared states of emergency, urging residents to stay at home.
"This is nothing to be trifled with," New York Governor Andrew Cuomo warned.
More than 2,400 flights had been cancelled nationwide and more than 4,000 delayed, while icy roads caused traffic deaths in Michigan, Kentucky, Indiana and Illinois.
The community of Embarrass, Minnesota notched a reading of minus 38C, the lowest temperature recorded in the United States outside Alaska on Friday, according to the National Weather Service.
"Temperatures tonight and tomorrow are expected to be extremely low, and dangerously so," said Massachusetts Governor Deval Patrick. "These are dangerous conditions."
New York City's Department of Homeless Services went to "code blue," doubling the number of vans patrolling streets to seek people who needed shelter.
In Washington, the Office of Personnel Management told hundreds of thousands of federal workers they could work from home or take a leave because of the storm.
The storm was reportedly a factor in multiple deaths, including a 50-year-old woman who lost control of her car on icy roads in Kentucky, an elderly woman with Alzheimer's who was not dressed for the cold in New York State, and a Philadelphia city worker crushed by a mound of rock salt.
The stormy weather began rolling in on Thursday, just a day after New York Mayor Bill de Blasio was sworn in to lead the nation's largest city.
De Blasio, who in 2010 criticised predecessor Mayor Michael Bloomberg for his handling of a post-Christmas storm, said 1,700 snowplows and 450 salt spreaders had hit the streets.
"I feel great about the response," De Blasio said on Friday after shovelling the pavement outside his Brooklyn home. "We are not out of this yet."
Forecasters said temperatures would plummet to minus 23C in the northeast while another wave of cold air was already moving through the Midwest after coming down from Canada.
Minnesota Governor Mark Dayton on Friday ordered all public schools statewide to close on Monday due to the expected extremely low temperatures, with forecasters predicting a low of minus 32C in Minneapolis on Sunday night.