The four were attempting to climb the 26,790-foot (8,167-meter) peak of Mount Dhaulagiri and have been missing since Tuesday.

Dhaulagiri is the seventh highest mountain in the world.

Chief of Nepal's mountaineering department Baburam Bhandari said the helicopter was sent early in the morning to the mountain. There has been no sign of the four so far.

The Japanese are Osamu Tanabe, 49, Toshio Yamamoto, 36, and Daisuke Honda, 32, all from Tokyo. The Sherpa guide is Pasang Gyelu.