An incident at the airport in Denver on US, when a Frontier Airlines aircraft struck a pedestrian on the runway as it was preparing for takeoff.

According to initial reports, the person in question was on runway 17L, but it is not yet clear how he came to be on the scene. Authorities said it is not believed to be an airport employee.

The incident caused consternation among both crew and passengers, and seconds after the collision the pilot contacted the control tower saying: “We’re stopping on the runway,” the pilot told the control tower, as heard in the posted dialogue. “We just hit someone. We have engine fire.”

Frontier Airlines confirmed that the crew aborted the takeoff as smoke was detected in the cabin after the tragic incident.

12 passengers injured

The evacuation procedure was carried out under pressure, resulting in minor injuries to 12 passengers. Five of them were taken to local hospitals for precautionary examinations and further care.

In a statement, the airline said it is working with the appropriate authorities to clarify the circumstances of the crash.

“We are investigating the incident and gathering more information in coordination with the airport and other safety authorities,” the airline said.

The Denver airport immediately notified the U.S. National Transportation Safety Board, and the runway where the tragedy occurred remained closed for several hours while the initial investigation was completed.

Authorities continue to review security camera footage and control tower communications to determine how the pedestrian was found on the active runway.