Washington Fire Chief, John Donnelly told a press briefing that emergency crews, totaling about 300 people, were working in extremely rough conditions and gave little indication they expected to find anyone alive.
A massive search and rescue operation was in progress, with divers visible in the glare of powerful lights as they plunged into the snow-lined Potomac to scour the wreckage of both aircraft.
Washington Mayor Muriel Bowser told reporters they are going be out there as long as it takes.
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The Bombardier plane, operated by an American Airlines subsidiary, was approaching Reagan National Airport at around 0200 GMT after flying from Wichita, Kansas, when the collision happened.
US Army officials said the helicopter involved was a Black Hawk carrying three soldiers on a training flight.
Witness Ari Schulman was driving home when he saw what he described as a stream of sparks overhead.
It was learnt that US Figure Skating said several athletes, coaches, and officials were aboard the flight, while officials in Moscow confirmed married Russian couple Evgenia Shishkova and Vadim Naumov — who won the 1994 world pairs title — were also on the jet.