Heavy snow and blizzard conditions are forecast to hit the US northeast, blanketing New York, Boston and beyond with up to a foot of snow.

With parts of the region already hit by a strong winter system over the weekend, residents braced for what the National Weather Service called possible "heavy snow and strong wind, even blizzard conditions".

"A blizzard watch is in effect for Long Island (New York) and coastal Massachusetts. Winter storm watches stretch from Delaware to Maine," the NWS said Sunday, referring to a large swath of the US northeast.

Six to 12 inches of accumulation were possible for the US state of New Jersey up to eastern Massachusetts, the NWS said. Four to eight inches were expected further south in parts of Maryland and Pennsylvania.

The US Weather Channel referred to the cold blast as a "possibly historic" winter storm that would likely result in flight cancellations, delays and possible airport closures late Monday to Tuesday.

Boston, New York, Philadelphia and Washington, meanwhile, were already preparing for the system, USA today reported.

Ahead of the weekend's heavy snow, Boston Mayor Marty Walsh called on people in the city to try to be helpful to each other.

"We ask that each and every single Boston resident look after their neighbour, be it someone you see outdoors or someone living next door," he said.