Smoke inside the cabin of a Delta Air Lines flight forced passengers to evacuate the plane via emergency slides and over-wing exits Tuesday in Denver.
Flight 1854, an MD-90 twin-engine airliner flying from Detroit to Denver International Airport, was carrying 146 passengers, a Delta spokesman said.
There were no reports of fire. Some passengers suffered minor injuries, according to the airline. A small number of passengers were treated and released, the airline said.
One passenger tweeted that "fumes came through the vents."
Another passenger said the cabin filled with smoke as the plane landed.
"The oxygen masks never came down and people began to freak out," D.J. Semenza told CNN. "The crew tried to keep calm and eventually called for an evacuation."
The smoke was detected prior to the plane reaching the gate, said Denver International Airport spokeswoman Emily Williams. Passengers were bused to the terminal.
"The safety of Delta's customers and crew is our top priority and we apologize for the concern this situation has caused," Delta said Wednesday in a statement.
Delta blamed the smoke on a small amount of hydraulic fluid dripping onto the aircraft's auxiliary power unit -- a small jet engine located in the rear of the plane. The APU is usually activated while aircraft are on the ground as a way to generate electricity.
When the fluid made contact with the hot APU, it created smoke, which was blown into the cabin, the airline said.