The small plane was flying from the tourist town of Pokhara, some 200 km northwest of the capital, Kathmandu, to Jomsom, about 80 km to the northwest, they told Reuters.
It is operated by Tara Air which mainly flies Canadian-built Twin Otter planes.
An airline official said the plane was carrying four Indians and two other foreigners, though their nationality was not known.
Nepal, home to the world's highest mountain, does have a record of accidents on its extensive domestic air network, with changeable weather and airstrips in difficult mountain locations.