Transport officials are investigating why a passenger jet was permitted to take off as Marine One approached with the US president on board.

The National Transportation Safety Board and the Federal Aviation Administration confirmed on Wednesday that they had launched an investigation into the matter.

Poor communication between the military and civilian air traffic controllers at Reagan has previously proved to be an issue.

Last year, 67 people lost their lives when an airliner collided with an Army Black Hawk helicopter.

In response, the FAA ruled that all take-offs and landings at the Washington, DC airport would be suspended whenever a helicopter passes on a conflicting flight path.

The airspace surrounding the White House and Reagan remains heavily congested with both military and commercial aircraft.

Crucially, the two aircraft were not on a collision course, as the passenger jet was ascending above Marine One as the helicopter made its approach.

The FAA stated that "there was a momentary loss of separation after which the aircraft continued to move away from one another.

"The air traffic controller was in contact with both the commercial pilot and Marine One pilot during the loss of separation," the FAA added.

The White House confirmed that Trump was never in any danger.

"Marine One flights are piloted by some of the best aviators in the world, and at no point was the President in harm's way," White House spokesperson Kush Desai said in a statement.

The Marine Corps stood by the conduct of their helicopter pilots.