Two Chinese passengers were among the victims of Wednesday evening's midair collision between a regional jet and a US Army helicopter into the Potomac River, the Chinese embassy in the United States said on Thursday, as an investigation is under way into the deadliest US air disaster since 2001.

The embassy said that based on "preliminary information", it learned that two Chinese citizens were among the victims of the plane collision accident.

"The embassy expresses its deep condolences to all the victims and expresses its deep condolences to the families. The embassy has asked the US side to verify the relevant situation and formally inform the Chinese side of the situation," the embassy spokesperson said in a statement.

The National Transportation Safety Board (NTSB), a federal agency responsible for investigating civil transportation accidents, said on Thursday that it would "leave no stone unturned" in the probe and urged the public not to "speculate" about the cause of the fatal collision.

The accident involved an American Airlines Bombardier CRJ-700 out of Wichita, Kansas, which carried 60 passengers and four crew members, and an Army Black Hawk helicopter with three military personnel on board during a training flight.

The plane was approaching a runway at Ronald Reagan National Airport in Arlington County, Virginia, just across the Potomac from Washington, before the collision.

"Sadly, there are no survivors," US President Donald Trump said at a news conference at the White House on Thursday. "This was a dark and excruciating night in our nation's capital and in our nation's history, and a tragedy of terrible proportions."

The names of all the victims had not yet been released by Thursday evening, but Dmitry Peskov, a spokesman for the Kremlin, confirmed that Russian former world figure skating champions Evgenia Shishkova and Vadim Naumov were passengers on the plane, according to the TASS news agency.

Andrew Eaves, one of the pilots of the helicopter, died in the crash, according to a Facebook post by his wife, the Magnolia Tribune in Mississippi reported.

The passengers also included members of the Skating Club of Boston, who were returning from the 2025 US Figure Skating Championships in Wichita, according to US media reports.

Trump criticized the helicopter pilots and suggested air traffic controllers were to blame.

But Jonathan Koziol, chief of staff for Army aviation, said the crew flying the helicopter was "very experienced".

The crew members were familiar with the unit and the daily congested airspace around Washington DC, Koziol said in a briefing on Thursday.

Trump, who took office 10 days ago, has moved quickly to cancel federal diversity initiatives. Asked if the crash was caused by diversity hiring, he said: "It just could have been."

The Trump administration has not provided any proof to back the assertions, and there is no evidence that efforts to make the federal workforce more diverse have compromised air safety, according to a Reuters report.

At a news conference on Thursday, NTSB chair Jennifer Homendy said the board will "conduct a thorough investigation of this entire tragedy, looking at the facts".

"We look at facts on our investigation and that will take some time," she said.

Investigators said they would have a preliminary report within 30 days.

"Our investigators are continuing to pull all that information, their personnel records, their files, where they were at, whether they were fatigued. All that information will be part of that investigative process," Brice Banning, a senior aviation accident investigator, said at the briefing. 

"But right now, we can't speculate on anything that may have been reported in the media until we get the opportunity to validate and understand how it impacts the investigation," he said.

The New York Times reported that staffing at the air traffic control tower at the airport was "not normal for the time of day and volume of traffic", according to an internal preliminary Federal Aviation Administration safety report about the collision that the Times reviewed.

The controller who was handling helicopters in the airport's vicinity Wednesday night was also instructing planes that were landing and departing from its runways. Those jobs typically are assigned to two controllers, rather than one, according to the report.

One day before the crash, another jet trying to land at the airport had to make a second approach after a helicopter emerged near its flight path, according to an audio recording from air traffic control, The Washington Post reported on Thursday. The Republic Airways flight 4514 did land safely, the Post reported, citing flight tracker maps.

The road around Hains Point, near the section of the Potomac River where wreckage of the plane and the helicopter were spotted, was closed Thursday morning.

As of Thursday evening, Washington DC Fire and EMS Chief John A. Donnelly said an estimated 40 bodies had been recovered from the Potomac River.

By around 11 am Thursday, planes began arriving and departing from the airport, which was closed for approximately 14 hours after the crash.

Dozens of reporters livestreamed accounts from Potomac Park's edge, near Ohio Drive, where they could see the airport but not the wreckage of either aircraft.