Three soldiers were onboard the helicopter, an Army official said.

There was no immediate word on the cause of the collision, but all takeoffs and landings from the airport were halted as dive teams scoured the site and helicopters from law enforcement agencies across the region flew over the scene in methodical search for bodies.

“We are going to recover our fellow citizens,” District of Columbia Mayor Muriel Bowser said at a somber news conference at the airport Thursday morning in which she declined to say how many bodies had been recovered.

Sen. Roger Marshall of Kansas said, “When one person dies it’s a tragedy, but when many, many, many people die it’s an unbearable sorrow.”

President Donald Trump said he had been “fully briefed on this terrible accident” and, referring to the passengers, added, “May God Bless their souls.”

The Federal Aviation Administration said the midair crash occurred before 9 p.m. EST when a regional jet that had departed from Wichita, Kansas, collided with a military helicopter on a training flight while on approach to an airport runway. It occurred in some of the most tightly controlled and monitored airspace in the world, just over three miles south of the White House and the Capitol.

Investigators will try to piece together the aircrafts’ final moments before their collision, including contact with air traffic controllers as well as a loss of altitude by the passenger jet.

American Airlines Flight 5342 was inbound to Reagan National at an altitude of about 400 feet and a speed of about 140 miles per hour when it suffered a rapid loss of altitude over the Potomac River, according to data from its radio transponder. The Canadian-made Bombardier CRJ-701 twin-engine jet, manufactured in 2004, can be configured to carry up to 70 passengers.

A few minutes before landing, air traffic controllers asked the arriving commercial jet if it could land on the shorter Runway 33 at Reagan National and the pilots said they were able. Controllers then cleared the plane to land on Runway 33. Flight tracking sites showed the plane adjust its approach to the new runway.

Less than 30 seconds before the crash, an air traffic controller asked the helicopter if it had the arriving plane in sight. The controller made another radio call to the helicopter moments later: “PAT 25 pass behind the CRJ.” Seconds after that, the two aircraft collided.

The plane’s radio transponder stopped transmitting about 2,400 feet short of the runway, roughly over the middle of the river.

Video from an observation camera at the nearby Kennedy Center showed two sets of lights consistent with aircraft appearing to join in a fireball.

“I know that flight. I’ve flown it several times myself,” said Sen. Jerry Moran of Kansas. He said he expected that many people in Wichita would know people who were on the flight.

“This is a very personal circumstance,” he said.

The collision occurred on a warm winter evening in Washington, with temperatures registering as high as 60 degrees Fahrenheit, following a stretch days earlier of intense cold and ice. On Wednesday, the Potomac River was 36 degrees Fahrenheit, according to the National Oceanic and Atmospheric Administration. The National Weather Service reported that wind gusts of up to 25 mph were possible in the area throughout the evening.

American Airlines CEO Robert Isom expressed “deep sorrow” for the crash and said the company was focused on the needs of passengers, crew, first responders and families and loved ones of those involved.

Some 300 first responders were on scene. Inflatable rescue boats were launched into the Potomac River from a point along the George Washington Parkway, just north of the airport, and first responders set up light towers from the shore to illuminate the area near the collision site. At least a half-dozen boats were scanning the water using searchlights.

“It’s a highly complex operation,” said D.C. fire chief John Donnelly. “The conditions out there are extremely rough for the responders.”

The U.S. Army described the helicopter as a UH-60 Blackhawk based at Fort Belvoir in Virginia. The helicopter was on a training flight. Military aircraft frequently conduct training flights in and around the congested and heavily-restricted airspace around the nation’s capital for familiarization and continuity of government planning.

The crash is serving as a major test for two of the Trump administration’s newest agency leaders. Pete Hegseth, sworn in days ago as defense secretary, posted on social media that an investigation has been “launched immediately” by the Army and the Defense Department. Transportation Secretary Sean Duffy, just sworn in earlier this week, said at a somber news conference at the airport early Thursday that his agency would provide all possible resources to the investigation.

The last fatal crash involving a U.S. commercial airline occured in 2009 near Buffalo, New York. Everyone aboard the Bombardier DHC-8 propeller plane was killed, including 45 passengers, 2 pilots and 2 flight attendants. Another person on the ground also died, bringing the total death toll to 50. An investigation determined that the captain accidentally caused the plane to stall as it approached the airport in Buffalo.

Reagan Airport will reopen at 11 a.m. Thursday, the Federal Aviation Administration announced. The FAA has previously said it would be closed until 5 a.m. Friday.

Located along the Potomac River, just southwest of the city. Reagan National is a popular choice because it’s much closer than the larger Dulles International Airport, which is deeper in Virginia.

Depending on the runway being used, flights into Reagan can offer passengers spectacular views of landmarks like the Washington Monument, the Lincoln Memorial, the National Mall and the U.S. Capitol. It’s a postcard-worthy welcome for tourists visiting the city.

The incident recalled the crash of an Air Florida flight that plummeted into the Potomac on January 13, 1982, that killed 78 people. That crash was attributed to bad weather.