The pilot and four of the six passengers, including a 68-year-old Japanese man, were among those killed, said police official Basanta Kuwar. Another passenger was missing, while a woman survived the crash, he said. Her condition was not immediately clear.
Rescuers were attempting to transport the injured woman out of the crash site, but think fog and rain was hampering efforts, Kuwar said, AP reported.
He said rescuers were also scouring the area for the missing person but bad weather and the mountainous terrain were making the operation difficult.
Aside from the Japanese man, all others aboard the helicopter were Nepalese.
The area where the crash happened is about 80 kilometers (50 miles) northwest of the capital, Kathmandu.
The Airbus-manufactured Ecureuil helicopter belongs to Altitude Air in Nepal and has been used in mountain rescues.