Nepal has deployed specialised mountain rescue guides and technical equipment to help search for people trapped in difficult terrain following devastating floods in the northern district of Rasuwa, after days of appeals from the country's mountain guiding community.

The operation, believed to be the first of its kind involving Nepal's professional mountain guides in a large-scale disaster rescue, was approved by the government on Friday.

The Nepal National Mountain Guide Association (NNMGA) had urged the Home Ministry and the Nepal Army's rescue command to deploy its members, saying their technical skills could help reach people stranded in steep and inaccessible areas.

NNMGA president Tul Singh Gurung wrote publicly to authorities warning that an estimated 100 to 200 people could be trapped inside a tunnel at the Melung Hydropower Project in Rasuwa.

"Due to the difficult terrain, steep surroundings, and confined access, evacuating a large number of people individually by small helicopters may be difficult, time-consuming and potentially risky," he said in the appeal.

The association said its teams could be inserted by helicopter using longline and drop-off operations onto ridges or steep terrain near the tunnel before establishing evacuation routes using fixed ropes, multi-point anchors and other technical rope-rescue systems.

NNMGA-certified guides had been waiting at Kathmandu airport for days to volunteer for the operation, but were initially not called upon.

"I think the government did not understand our offer," NNMGA treasurer Abiral Rai said on Thursday before some of the volunteers returned home after failing to secure a role in the rescue effort.

The government approved the deployment on Friday, with technical equipment provided by the Nepal Mountain Instructors Association and specialist personnel drawn from the NNMGA.

The Nepal Mountaineering Association said it was coordinating the mobilisation of several rescue teams in support of the Nepal Army and other government agencies.

The operation includes two helicopter longline rescue teams and ground support teams, the association said.

Two rescuers -- IFMGA mountain guide Bikram Karki and aspirant guide Geshman Tamang, who is also operating a drone -- were already at the disaster site.

Another helicopter team, including longline rescue expert Pemba Wangchu Sherpa and three other mountain guides and aspirant guides, had reached the airport and was preparing for deployment.

Two additional teams were travelling by vehicle towards the affected area.

"This could provide a safer and more efficient route for assisting trapped people out of the affected area and moving them toward a secure evacuation point," Rai said.

Nepal's internationally trained mountain guides are accustomed to technical operations involving helicopters, ropes and steep terrain, skills that rescue groups say could prove crucial as authorities struggle to reach people cut off by the floods.

The deployment marks the first time such specialised mountain guiding teams have been formally mobilised for a major technical rescue operation involving people trapped in difficult terrain and tunnels, the associations said.