Governors of some states expected to be walloped by a monster storm heading into the U.S. Northeast have issued travel bans on roads.

New York Gov. Andrew Cuomo announced a travel ban on roads in 13 state counties starting at 11 p.m. in advance of the storm. The ban includes New York City and Long Island.

"It's dangerous to be out there now," he said at a news conference. "It's only going to become more dangerous. And at one point it's irresponsible."

Cuomo said those found travelling on the roads could face fines of up to $300 US.

Cuomo said the Port Authority and subway system would be closed at 11 p.m. Parts of New York are expected to be hit with 45 to 60 centimetres of snow.

In Connecticut, Gov. Dannel Malloy issued a travel ban across the whole state "as a result of potential life-threatening conditions." Massachusetts Gov. Charlie Baker also issued a travel ban to take effect after midnight.

Emergency personnel are exempt from the travel restrictions.

The Philadelphia-to-Boston corridor of more than 35 million people began shutting down earlier Monday as the storm that could unload a paralyzing 30 to 90 centimetres of snow swirled into the Northeast.

Snow was blowing sideways with increasing intensity in New York City by midafternoon as flurries began in Boston. Forecasters said the storm would build into a blizzard, and the brunt of it would hit Monday evening and into Tuesday.

More than 5,800 flights in and out of the Northeast were cancelled, and many of them may not take off again until Wednesday. Schools and businesses let out early. State government offices closed.

And cities mobilized snowplows and salt spreaders to deal with the dangerously windy blast that could instantly transform what has been a largely snow-free winter in the urban Northeast.

All too aware that big snowstorms can make or break politicians, governors and mayors moved quickly to declare emergencies and order the shutdown of highways, streets and mass transit systems — perhaps for days — to prevent travellers from getting stranded and to enable plows and emergency vehicles to get through. The governors of New York, New Jersey, Massachusetts and Connecticut declared states of emergency.

"It is not a regular storm," New York Mayor Bill de Blasio said. "What you are going to see in a few hours is something that hits very hard and very fast."

Boston is expected to get 60 to 90 centimetres, New York 45 to 60 centimetres, and Philadelphia more than 30 centimetres. The National Weather Service issued a blizzard warning for a 400 kilometre swath of the region, meaning heavy, blowing snow and potential whiteout conditions.

'A top-5 storm'

Winter Weather Laguardia

A ticket agent waits for customers in a lightly trafficked LaGuardia Airport on Monday. Officials cautioned Northeast residents not to be misled by a relatively smooth Monday morning commute. (Seth Wenig/Associated Press)

"This could be a storm the likes of which we have never seen before," de Blasio told a news conference in a Manhattan sanitation garage where workers were preparing plows and salt for the massive cleanup on about 10,000 kilometres of city roadways.

"New Yorkers should not underestimate this storm. Assume conditions will be unsafe. Assume that you do not want to be out in this storm. When you can stay indoors, stay indoors; when you can stay off the roads, stay off the roads."

The governors of Massachusetts and Connecticut told residents to expect driving bans later tonight and all day tomorrow. They warned that hundreds of thousands of people could lose power, possibly for days.

"We are anticipating an historic, top-five storm, based on the snowfall," Massachusetts Gov. Charlie Baker told reporters on Monday.

The Boston-area transit system will be shut on Tuesday, he said. He warned that coastal parts of the state will likely suffer flooding.

President Barack Obama, who is travelling in New Delhi, India, was briefed on the coming storm earlier on Monday, White House spokesman Josh Earnest told reporters.

Estimated snowfall accumulations:

  • New York City: 45 to 60 cm
  • Boston: 61 to 91 cm
  • Hartford: 50 to 76 cm
  • Providence: 61 to 91 cm
  • Philadelphia: 25 to 36 cm

'Wintry misery'

The National Weather Service said the nor'easter would bring heavy snow, powerful winds and widespread coastal flooding starting Monday and through Tuesday. A blizzard warning was issued for a 400-kilometre stretch of the Northeast, including New York and Boston.

Snow in New York City

A worker pushes a snowblower down Lexington Avenue near Grand Central Terminal in New York City. (Carlo Allegri/Reuters )

"A cold surge of Canadian air is strengthening a system in Virginia and is now bringing snow to the most densely populated region of the U.S.," said Chris Murphy of The Weather Network. "As the low drifts out to sea, it is expected to catch a ride along the jet stream and spin its wintry misery northwards."

The storm system has the potential to affect as many as 60 million people.

"This is going to be a slow-moving storm ... this could be five-centimetre-an-hour kind of snowfall, so it's going to pile up very quick," Murphy said.

"Strong winds out of the northeast will buffet the coast, producing a surge capable of flooding and doing damage in areas that were pummelled by superstorm Sandy."

Flights cancelled

So far more than 2,600 flights scheduled for Monday have been cancelled, according to the flight tracking site FlightAware.

Winter Weather Virginia

The Winchester, Va., area is under a winter storm warning, with up to 20 centimetres of snow expected to fall in the next day. (Ginger Perry/The Winchester Star/Associated Press)

Another 3,300 flights have been scrapped for Tuesday — and the cancellations keep mounting.

Those affected most are the three airports serving New York City, though flights in Boston and Philadelphia were also cancelled.

Problems in the Northeast are also rippling outward.

In West Palm Beach, Fla., about 30 per cent of all flights have been cancelled. Fort Lauderdale and Orlando are also reporting major cancellations.

Most major airlines are allowing customers whose flights are cancelled in the next few days to book new flights without paying a penalty, though specific terms vary by airline.

Snowstorm vs. blizzard: What's the difference?

The National Weather Service issued a blizzard warning for a huge swath of the U.S.'s Northeast corridor, from New Jersey up to Massachusetts, meaning potential white-out conditions as heavy snow swirls amid gusting wind

The weather service says a blizzard includes sustained or frequent wind gusts of 35 m.p.h. (56 km/h) or greater and considerable falling snow that lasts for at least three hours.

This storm is expected to last up to 36 hours in some locations, forecasters said. But another storm could be looming ahead of next weekend.

5 biggest snowstorms at Central Park

  • February 2006: 68.3 cm
  • December 1947: 65.5 cm
  • March 1888: 53.3 cm
  • February 2010: 53 cm
  • January 1996: 51.3 cm

Source: U.S. National Weather Service

With files from CBC News and Reuters