Rescuers struggled through mud and debris for a sixth day, as the number of missing people soared to nearly 4,500 since tsunami-like glacial floods roared down from the China-Nepal border, creating an "unimaginable" disaster.

The deluge of ice and mud caused huge lakes to form, and one of these formations has become a direct threat to emergency workers scouring the region for survivors.

Rescue worker Kawan Koirala, from the Nepal Scout Disaster Response Team, said they were struggling in thick, leg-sucking mud.