The National Transportation Safety Board (NTSB) is collecting information about the evacuation of a Frontier Airlines aircraft after the jet struck and killed a person on the runway during departure from Denver international airport.

The flight, which was headed from Denver to Los Angeles international airport, “reported striking a pedestrian during takeoff at DEN at approximately 11:19 pm on Friday”, according to a statement posted on the airport’s official X account. The individual has not been publicly identified.

Passengers exited the aircraft using emergency slides before being transported back to the terminal by bus. An airport representative said 12 passengers sustained minor injuries, while five were hospitalized. No additional information was given about the nature of those injuries. However, several passengers voiced concerns about the evacuation process, saying they remained inside the aircraft for several minutes while smoke accumulated in the cabin and were later left outside on the tarmac in cold conditions.

“We are gathering information about the emergency evacuation to determine if it meets criteria for a safety investigation,” NTSB spokesperson Sarah Taylor Sulick told the Associated Press on Sunday.

The US transportation secretary, Sean Duffy, said Saturday that the individual who died was a “trespasser” who had breached airport security and “deliberately scaled a permit fence and ran out on to a runway”.

“The trespasser on the runway was then struck by Frontier Airlines flight 4345 during takeoff at high speed,” Duffy added in an X post. He also confirmed that 12 people had been injured, including five who required hospitalization. Firefighters also responded to the scene, he said.

Duffy said the investigation into the security breach would be led by local law enforcement, with assistance from the Federal Aviation Administration (FAA) and the Transportation Security Administration (TSA).

Frontier Airlines stated that the Airbus A321 involved in the incident “was carrying 224 passengers and seven crew members”. The airline added: “We are investigating this incident and gathering more information in coordination with the airport and other safety authorities.”

A video that appeared to be taken by a flight passenger and circulated on social media evidently showed the moment the person was struck. The video captured the sound of a loud crash as well as people screaming.

Friday’s incident at Denver international airport occurred just one day after a worker for Delta Air Lines was killed Thursday night at Florida’s Orlando international airport. According to local outlet WESH, the employee died after a vehicle hit a jet bridge adjacent to an aircraft carrying passengers.