Contact was lost with the plane a few minutes after it made an unscheduled fuel stop in the city of Pokhara on its flight from the capital, Katmandu, to the town of Jumla, said Civil Aviation Authority of Nepal official Ram Hari Sharma.
Another aviation official, Dharmendra Pandey, said villagers in Argakhachi district reported that the plane had crashed in a remote mountainous area. He said police were trying to reach the area.
The de Havilland Canada-manufactured Twin Otter plane had 15 passengers and three crew members on board. One of the passengers was believed to be a Danish national, while the rest on board, including a child, were Nepalese, Sharma said.
It was snowing this weekend in parts of the mountainous region, and visibility was low due to fog.
A rescue helicopter was trying to reach the area where contact with the plane was lost, but the weather conditions were making it difficult.
The plane was scheduled to fly directly from Katmandu to Jumla, about 400 kilometers (250 miles) to the west, but stopped to refuel at Pokhara's airport about a third of the way into the journey.
In May, another plane of the same make and model operated by state-owned Nepal Airlines crashed while attempting to land at a mountain airstrip in northern Nepal, injuring all 21 people on board.
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