"An Islander aircraft of the Nepal Army is missing since 7:05pm (1320 GMT)," he said. "It was returning from Nepalgunj to Kathmandu after a medical rescue and carrying six people including crew.
"The area from where it lost communication is identified as Dhorpatan National Park in Baglung district."
It has not been confirmed that the plane crashed but a witness in the area where it went missing told the state-run Nepal Television there was an explosion and fire.
The reserve -- the only location in Nepal where hunting is permitted -- has its headquarters in the village of Dhorpatan, on the southern slopes of Mount Dhaulagiri, around a four-day walk from the town of Balewa.
Nepal has no air force but flies several aircraft within the Nepalese Army Service, also known as the Nepal Army Air Wing.