NEW: Rescue teams are racing against the clock in Nepal as they search for survivors after a wall of water, mud and debris tears through communities near the Tibet border. At least 65 Americans are among those still missing, according to officials in Nepal.
"The floods came in suddenly and exploded like a bomb," one survivor says.
Security video shows people with only seconds to react as the flood sweeps away vehicles, buses and buildings. Officials now believe a powerful landslide, potentially triggered by part of a glacier breaking off, unleashed an avalanche of ice and rock that caused the flooding.
The Red Cross says at least 10,000 families have lost their homes, while buried roads and destroyed bridges are making some devastated areas accessible only by helicopter.