(CNN) -- A search is on for a missing Nepali sherpa who has summited Mount Everest 19 times.

The mountain guide went missing after an avalanche on Saturday, said the mountaineering agency for which he works.

An avalanche swept away Chuwang Nima Sherpa on 7,129-meter-high (23,389-foot-high) Mount Baruntse on Saturday afternoon, while he was fixing ropes for climbers at 7,045 meters (23,113 feet), said Jiban Ghimire of Sherpa Shangri-La Treks and Expeditions.

"Chuwang Nima was fixing ropes for another expedition in the mountain, because they asked for help, when the avalanche struck," Ghimire said.

Chuwang Nima was climbing with mountain guide Melissa Arnot, from the U.S. state of Idaho. The two had planned an alpine-style climb, without any support staff and fixed ropes or stops till the summit, Ghimire said.

A helicopter was dispatched to look for Chuwang Nima on Sunday morning, but had to return because of bad weather.

Chuwang Nima, 39, is well known in mountaineering circles, and climbs and trains in the United States as well.

He was in Denali National Park in Alaska for technical training and rescue operations during the summer, according to Ghimire.

Apa Sherpa -- a 50-year-old Nepali -- holds the record for summiting Everest, with 20 climbs.

Everest is the world's highest mountain above sea level, at 8,848 meters (29,029 feet).