A winter storm slammed into the U.S. Northeast with howling winds and frigid cold, dumping nearly 2 feet (60 centimetres) of snow in some parts and whipping up blizzard-like conditions Friday.
By Friday morning, about 1,900 flights were cancelled nationwide, according to the aviation tracking website FlightAware.com. Most were in New York, Philadelphia, Boston, Chicago and Washington, D.C.
Governors in New York and New Jersey declared states of emergency, urging residents to stay at home. Hundreds of schools were shut down in Boston and New York, extending the holiday break for tens of thousands of students.
"This is nothing to be trifled with," New York Gov. Andrew Cuomo said. "People should seriously consider staying in their homes."
The storm has led to at least nine deaths as it sweeps across the eastern half of the U.S. Slick roads have caused traffic deaths in Michigan, Kentucky, Indiana and Illinois.
A massive pile of salt fell on a worker at a Philadelphia storage facility, killing him. And authorities say a woman with Alzheimer's disease froze to death after she wandered away from her rural New York home.
Forecasters said temperatures were plummeting to well below freezing, and wind chill readings could hit minus 10 Fahrenheit (minus 23 Celsius).
Another wave of cold air already was moving through the Midwest after coming down from Canada.
Outreach teams were searching streets in New York City and Boston for homeless people at risk of freezing to death.
Some major highways in New York state were shut down overnight, and some commuter trains around New York City were operating on a reduced schedule. Amtrak planned to run trains on all of its Northeast lines on Friday but operate on a modified schedule, spokeswoman Christina Leeds said.
New Jersey Gov. Chris Christie ordered nonessential state workers to stay home Friday. State offices and courthouses were closed. State offices were also closed in Massachusetts.
The heavy weather began rolling in Thursday, just a day after New York Mayor Bill de Blasio was sworn in to lead the nation's largest city and a few days before Boston Mayor Thomas Menino ends 20 years in office.
De Blasio, who in 2010 criticized predecessor Mayor Michael Bloomberg for his handling of a post-Christmas storm, said 1,700 snowplows and 450 salt spreaders were hitting the streets in New York City.
"We have to get it right, no question about it," de Blasio said. "We are focused like a laser on protecting this city."
The snowstorm worked its way east from the Midwest, where it dropped up to 17 inches (431 millimeters) of snow in parts of Chicago and prompted the cancellation Thursday of hundreds of flights at both of the city's airports.