With Hurricane Irene bearing down on the East Coast, U.S. air carriers have canceled nearly 5,000 flights this weekend and warned that several major airports in New York and Washington could shut down entirely to guard against the storm’s destructive force.

Because the region is home to the nation’s busiest airspace, the cancellations are expected to cause delays at airports across the country starting today, stranding tens of thousands of travelers, many returning from summer vacations.

Amtrak, meanwhile, said it planned to cancel most train service south of Washington, D.C., through Sunday.

Officials at Los Angeles International Airport said all flights remained on schedule Friday but that routes to and from the East Coast could be delayed or canceled over the weekend as the first major hurricane of the 2011 season slams the Atlantic coastline.

Several airline officials predicted that most of the cancellations will take place Sunday, when the storm is expected to reach high-traffic airports, including New York’s John F. Kennedy International Airport and Dulles International Airport near Washington.

“Sunday will be the worst day,” said Tim Smith, a spokesman for American Airlines, which plans to cancel 265 flights primarily in Washington, New York, Virginia and North Carolina.

United and Continental airlines, owned by the same parent company, announced plans to cancel 2,300 East Coast flights combined. The airlines also said they would suspend all operations today and Sunday at JFK, nearby LaGuardia and Newark Liberty International airports.