ARLINGTON, Va. — A jet carrying 60 passengers and four crew members collided Wednesday with an Army helicopter while landing at Ronald Reagan National Airport near Washington, prompting a large search-and-rescue operation in the nearby Potomac River.

There was no immediate word on casualties or the cause of the collision, but all takeoffs and landings from the airport were halted as helicopters from law enforcement agencies across the region flew over the scene in search of survivors. Inflatable rescue boats were launched into the Potomac River from a point along the George Washington Parkway, just north of the airport, and first responders set up light towers from the shore to illuminate the area near the site of the collision.