The Switzerland-based International Federation of Red Cross and Red Crescent Societies (IFRC) launched the appeal for 25 million Swiss francs the day after releasing one million francs to support the immediate lifesaving response.

The appeal is to cover emergency disaster response followed by supporting the medium and long-term recovery, over the next two years.

"While we are getting a clearer picture of the scale of devastation, we know that entire villages were washed away and needs will grow in the coming hours and days," IFRC secretary general Jagan Chapagain said in a statement.

"Communities that have lost homes and livelihoods will need sustained support as they recover and rebuild."

The devastating tsunami-like wall of freezing water and mud wiped out towns under a torrent of sludge, engulfing homes, and smashing bridges and dams on Wednesday.

"Current estimates suggest around 93,000 people may have been affected, while assessments continue in hard-to-reach areas," the IFRC said.

"The remoteness of the affected areas, combined with damaged infrastructure, is making it harder both to assess the full scale of the disaster and to deliver assistance to people who need it most."

The appeal will support the local Nepal Red Cross team's response with shelter, cash assistance, household relief items, water, sanitation and hygiene, mental health and psychosocial support, and restoring family links.

NRC crews have already been providing food, water and emergency supplies including tarpaulins, blankets, first aid kits, stretchers and body bags, the IFRC said.

The IFRC is the world's largest humanitarian network.