Tens of millions of Americans from the US capital Washington to the northern state of Maine braced for the storm, with up to two feet (60 centimeters) of snow forecast in some areas.

The National Weather Service said blizzard conditions would "quickly materialize" from Maryland up to southeastern New England, making travel "extremely treacherous."

Snow could fall at a rate of two to three inches per hour at the peak of the storm, with nearly 54 million people in its path, it said.

Power outages are likely due to heavy snow and strong wind gusts, forecasters said.

In New York, which has more than eight million people, Mamdani said streets, highways and bridges would be shut down from 9:00 pm Sunday (0200 GMT) until noon Monday.

"New York City has not faced a storm of this scale in the last decade," he said, explaining the state of emergency.

"We are asking New Yorkers to avoid all non-essential travel."

The ban will not affect essential workers or New Yorkers needing to travel due to emergencies, according to Mamdani.

- 'Worst yet to come' -

New Jersey Governor Mikie Sherrill declared a state of emergency beginning midday Sunday, freeing up funds and allowing the swift deployment of resources to address the weather crisis.

In Boston, Mayor Michelle Wu closed all public schools and municipal buildings on Monday.

"We ask everyone to plan ahead, stay safe and warm, and stay off the roads to help our public works and public safety efforts," Wu said.

The National Weather Service said "moderate to major" coastal flooding affecting waterfront roads and properties was possible from Delaware up to Cape Cod in Massachusetts.

The storm comes just weeks after the region recovered from another devastating weather system that was linked to more than 100 deaths.

"The worst is yet to come," New York Governor Kathy Hochul told a press briefing Sunday.

"Whatever you need -- any groceries, any medicines you need to be refilled at the pharmacy, any pet food you need to have -- do it right now."

Then, she advised, "just settle in."

"Watch some more Olympics, read a book, catch up on the news, call your family members, call your moms -- especially your moms."