An American Airlines plane and a U.S. Army helicopter collided near Reagan National Airport and crashed into the Potomac River, according to officials.

All 64 people aboard an American Airlines jet that collided with an Army helicopter were feared dead in what was likely to be the worst U.S. aviation disaster in almost a quarter century, officials said Thursday.

An American Airlines plane carrying 60 passengers and four crew members collided with an Army Black Hawk helicopter outside Reagan National Airport near Washington, D.C. Wednesday evening. Three soldiers were onboard the helicopter and a massive search and rescue operation is now unfolding in the Potomac River.