A US passenger plane carrying 64 people crashed into Washington DC's chilly Potomac River after colliding midair with a military helicopter on a nighttime training exercise Wednesday, prompting a major emergency response and the grounding of all flights.

The plane had been about to land at nearby Reagan National Airport after flying from Kansas.

American Airlines, whose subsidiary operated the flight, said "there were 60 passengers and four crew members on board the aircraft."

A US Army official said the helicopter involved was a Black Hawk model carrying three soldiers -- their status currently unknown. They had been on a "training flight," a separate military spokesperson said in a statement.

Washington police said "there is no confirmed information on casualties at this time."

However, a massive search and rescue operation was in progress, with divers visible as they plunged into the snow-lined Potomac.

The Washington Post quoted unnamed sources saying police had started to pull multiple bodies from the water.

Witness Ari Schulman described "a........

© International Business Times