People from North Carolina to Massachusetts are being warned to be ready to be slammed by a major winter storm starting Wednesday.
"This is going to be a serious storm — and people need to take it seriously," New York City Mayor Bill de Blasio warned at a briefing Tuesday.
Parts of the city could see as much as a foot of snow, and communities to its north, as well as northern New Jersey and parts of Connecticut, may get even more than that.
More from NBC News:
Biggest snowstorm in years on track to bury parts of the Northeast
White House counsel's office warned Trump not to fire Chris Wray
California orders thousands of body bags as Covid death toll grows
The snowstorm could be the biggest New York City has seen in years, De Blasio said as officials, including the MTA, urged people to avoid traveling unless necessary.
Those warnings were echoes as far south as North Carolina, where the state's emergency management agency urged drivers to use caution if they must be on the roads. In northern North Carolina, a mix of snow, sleet and freezing rain Wednesday morning was expected.
Northwestern Virginia could get snow and sleet and up to a quarter-inch of ice, according to the National Weather Service, and Maryland activated a statewide response for a storm that could see a foot of snow in Hagerstown.
In Boston, forecasters are calling for up to a foot of snow, which is expected to start falling around sunset. New York City's weather service office predicted snow Wednesday afternoon and into Thursday morning.
Pennsylvania Gov. Tom Wolf signed a proclamation of a disaster emergency ahead of the storm, which authorizes state use of resources and purchases.
Allentown, Pennsylvania, might get as much as 18 inches of snow, forecasters said. Harrisburg and Williamsport could get even more than that, with a forecast late Tuesday predicting between 18 inches and 2 feet.
Pennsylvania, like other states, is distributing a Covid-19 vaccine, and state officials say they are prepared to deal with any impacts from the storm and to keep roads clear.
"There's actually something simple that every Pennsylvanian can do to help us all get through this storm as quickly as possible," Wolf said. "And that is: Stay home, if you can."