Massive flash floods in a border area of Nepal and China on Wednesday killed at least 160 people and left hundreds of tourists, workers, and others missing.

Experts said an avalanche from a glacier was the likely cause in the warming Himalaya region. Police in Nepal reported at least 157 dead. China’s state broadcaster CCTV reported at least three dead and 265 missing in the Tibet region’s Gyirong County near the border. Drone footage showed roads destroyed and buildings buried by thundering water the colour of wet cement. State news agency Xinhua reported significant casualties.

The region’s steep valleys are economic lifelines and travel corridors but are precarious when disaster strikes. Images showed what appeared to be the second floors of buildings in Nepal’s hard-hit Nuwakot district slathered in mud after the torrent rushed by. Debris hung from tree branches and wires, vehicles were buried, and some stunned survivors were caked in mud. There was little time for anyone to flee.