A powerful winter storm has begun striking the northeastern United States, placing about 59 million people under weather alerts. The storm has caused widespread travel disruption, with more than 5,000 flights canceled and around 600 delayed across the country, according to flight tracking website FlightAware. New York City has issued a travel ban, while several states including Massachusetts, Connecticut, Delaware, New Jersey, and Rhode Island have declared states of emergency.

FlightAware reported that the highest number of cancellations occurred at New York’s John F. Kennedy (JFK) and LaGuardia airports. JetBlue Airways said it had already canceled 776 flights and warned passengers of significant disruptions and cancellations through February 24. The National Weather Service forecast that the storm would affect the U.S. Northeast and much of the Canadian Maritimes from Sunday evening through Monday.

Forecasters described the system as potentially the strongest “nor’easter” in nearly a decade, warning of heavy snowfall, strong winds, and coastal flooding across affected areas.