A United Airlines plane bound for Denver was forced to make an emergency landing in Aspen on Sunday, as smoke poured into the cabin a few minutes into the flight.

United Express Flight 5940, operated by SkyWest, took off from the Aspen/Pitkin County Airport with 65 passengers aboard at 12:49, but was forced to return to the airport moments later.

A malfunctioning air conditioning system was blamed by officials, with passengers reporting smoke billowing into the cabin.

No injuries were reported following the incident.

The airport was closed as a precaution while the situation was investigated, confirmed airport director Jim Elwood. Delays were subsequently reported at the location.

Passengers were offered counselling while waiting in the terminal for the plane to be repaired.

The aircraft - a Canadair Regional Jet 700 Series (CRJ-700) - took off from Aspen for the second time at about 16:30, landing safely in Denver shortly after 17:00, said SkyWest spokeswoman Marissa Snow.