Hundreds of foreign tourists are reported missing after devastating flooding in Nepal struck an area popular with international travellers.

The Nepal Tourism Board said on Thursday that 644 tourists were out of contact, including 517 foreign nationals. They include visitors from 19 European countries as well as China, the United States and Australia.

It is urging travellers to inform the nearest police or security authority, local administration, travel agency, guide or tour operator of their location and in a statement said "please remain clam, stay informed and follow official safety instructions".

The disaster has particularly affected Rasuwa and neighbouring Nuwakot, north of Kathmandu and close to Nepal's border with Tibet.

Nepal has long been one of Asia's most popular destinations for backpackers, hikers and adventure travellers, attracted by its dramatic Himalayan landscape, relatively affordable travel and combination of mountain trekking, historic cities and Buddhist and Hindu culture.