The pilots of a Frontier Airlines plane were forced to abort a takeoff at Denver International Airport late Friday after what they described as a collision with a person on the runway, the airline said.

The Airbus A321 jet, with 224 passengers and seven crew, was leaving on Flight 4345 to Los Angeles International Airport when the collision happened, Frontier Airlines said in a statement. Smoke was then reported from inside the plane and the passengers were safely evacuated using emergency slides as a precaution, it added.

“We’re stopping on the runway,” a pilot told the air traffic control tower, according to a recording posted by the ATC.com app. “We just hit somebody. We have an engine fire.” Later, a pilot told the tower that “an individual was walking across the runway.”

The crew told air traffic control that they were evacuating the plane on the runway because of smoke inside.

Denver airport said in a statement that the incident happened at about 11:20 p.m., and that firefighters put out an engine fire on the plane. The passengers were taken back to the terminal by bus, it added.

The plane came to a sudden stop on the runway soon after it had started accelerating for takeoff, according to a data replay from the tracking website Flightradar24.

The airport and the airline did not provide any details about the identity or condition of the person the pilots said was struck.

Frontier’s headquarters are in Denver. The airline and the airport both said that investigations into the incident were underway. The airport said the National Transportation Safety Board had been notified.

Denver airport did not report major disruptions to flight operations. Runway 17L, which was closed after the incident, is one of six runways at the airport.