The total flight time was supposed to be 19 minutes, but contact was lost eight minutes after takeoff.
Eighteen passengers and three crew members were on the plane, Rai said. The passengers include two foreigners -- one Chinese and one Kuwaiti.
Rai said the weather Wednesday morning was clear when the plane took off. He said the Twin Otter plane was new, imported from Canada last September.
An army helicopter and two private helicopters have been deployed in the search.