Officials provided no death toll from Wednesday night's collision but U.S. Senator Roger Marshall of Kansas, from where the flight was traveling, suggested most if not all those on board had been killed.
"It's really hard when you lose probably over 60 Kansans simultaneously," he told a press conference at Reagan airport in the U.S. capital early on Thursday.
"When one person dies, it's a tragedy, but when many, many, many people die, it's an unbearable sorrow. It's a heartbreak beyond measure."
American Airlines confirmed 60 passengers and four crew members were aboard the jet. The helicopter, on a training flight, was carrying three soldiers, a U.S. official said.
CBS News, citing a police official, said at least 18 bodies had been recovered and reported that a dive team had recovered one of the two data recorders, the so-called black boxes, from the plane.
Two sources told Reuters multiple bodies had been pulled from the water.
The midair collision occurred as the passenger jet, traveling from Wichita in Kansas, was on approach to land at Reagan. Radio communications between the air traffic control tower and the Black Hawk showed the helicopter crew knew the plane was in the vicinity.
The Pentagon said it was launching an investigation.
In a post on Truth Social, President Donald Trump questioned the actions of the helicopter crew and air traffic controllers on what he described as a clear night.
"This is a bad situation that looks like it should have been prevented. NOT GOOD!!!," he wrote.
Air traffic control recordings appear to capture the final attempted communications with the helicopter, call sign PAT25, before it collides with the plane, described as CRJ.
"PAT25, do you have a CRJ in sight? PAT25, pass behind the CRJ," an air traffic controller says at 8:47 p.m. (0147 GMT), according to a recording on liveatc.net.
Seconds later, another aircraft calls in to air traffic control, saying, "Tower, did you see that?" - apparently referring to the crash. An air traffic controller then redirects planes heading to runway 33 to go around.
Webcam video of the crash showed the collision and an explosion lighting up the night sky.
"I just saw a fireball and then it was just gone. I haven't seen anything since they hit the river," an air traffic controller was heard saying over the radio.
RESCUE EFFORTS
Relatives gathered at the airport said they were receiving little official information. One man wept as he stood on the sidewalk at 3 a.m. outside the airport.
The plane carried a number of U.S. ice skaters, family members and coaches returning from a camp following figure skating championships in Wichita, governing body U.S. Figure Skating said.
Among those on board were Russian former figure skatingworld champions Yevgenia Shishkova and Vadim Naumov, Russian state media reported. The Kremlin offered condolences to the families of Russians killed, and said there were no plans for contacts for now between President Vladimir Putin and Trump.
Washington DC fire chief John Donnelly said at least 300 first responders were continuing to work on the "highly complex" rescue operation.
"Conditions out there are extremely rough for the responders," Donnelly said. "It's cold. They're dealing with windy conditions."
Asked whether there were any survivors, he said: "We don't know yet."
Hypothermia is a concern for any possible survivors and first responders.
"At these frigid water temperatures, the human body’s core temperature quickly drops. Exhaustion or unconsciousness can occur in as little as 15 to 30 minutes," AccuWeather Senior Director of Forecast Operations Dan DePodwin said.
Airports authority CEO Potter said the airport would remain closed until at least 11 a.m. on Thursday.
In 1982, Air Florida Flight 90 crashed into the 14th Street Bridge over the Potomac River, killing 70 passengers and four crew members. Only four passengers and one crew member survived.
The last deadly major crash involving a commercial airliner in the U.S. was in 2009, when all 49 people aboard a Colgan Air flight died when the plane crashed in New York state. One person was also killed on the ground.
A series of near-miss incidents in recent years has raised safety concerns.
American Airlines Flight 5342 was operated by PSA Airlines, American's Ohio-based regional subsidiary, the FAA said.
"We're cooperating with the National Transportation Safety Board in its investigation and will continue to provide all the information we can," American Airlines CEO Robert Isom said.
