Expedition organiser Mingma Sherpa said that the five went missing possibly after an avalanche on Monday.
Tourism ministry officials say it happened as they descending from the summit of the 8,586m high mountain.
Mr Sherpa said those feared dead were from South Korea, Hungary and Nepal, and he was not optimistic of finding them alive.
“All our efforts to trace them have failed,” he told the BBC. “The weather is bad and we’ve run out of resources to recover their bodies.”
He said that rescue helicopters flown to the area since they went missing had also failed to locate them.
The five were identified as South Korean Namsoo Park, 47, Hungarians Zsolt Eross, 45, and Peter Kiss, 27, and two Nepali high altitude workers – Bibash Gurung, 24, and Pho Dorchi, 23.
Straddling the border between Nepal, India and China, Kanchenjunga is the third highest mountain in the world and is considered to be technically challenging with high chances of blizzards and avalanches.