A powerful winter storm swept across New York City and much of the northeastern United States on Monday, trapping millions indoors under blizzard warnings and strict travel bans, while forcing the cancellation of thousands of flights.

Heavy snow fell at a rate of 2 to 3 inches per hour from New York to Massachusetts early Monday, with several areas accumulating more than a foot since Sunday. Strong wind gusts topping 30 mph created whiteout conditions and dangerously low visibility.

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Air travel faced massive disruption, with more than 5,000 flights canceled nationwide on Monday, according to flight tracking service FlightAware. The bulk of the cancellations occurred at major airports in New York, New Jersey and Boston, stranding travelers and halting operations across key hubs.

Blizzard warnings were in effect from Maryland to Maine. Authorities in New York City issued emergency alerts banning non-essential road travel through noon Monday due to hazardous conditions. Similar restrictions were enforced in Rhode Island and New Jersey.

Long Island MacArthur Airport recorded 22.5 inches of snow, while parts of New York City saw up to 16 inches. Freehold, New Jersey, reported 22 inches, and communities in Connecticut and Rhode Island received up to 17 inches.

Public transportation was suspended in some areas, and delivery services paused operations as conditions worsened.

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The storm also triggered widespread power outages, leaving more than 400,000 customers without electricity along the East Coast early Monday. States and major cities across the region declared emergencies as crews worked to clear roads and restore power.

Forecasters described the system as a “classic bomb cyclone/nor’easter,” warning that the combination of heavy snowfall and powerful winds could continue to cause severe disruptions before tapering off later in the day.