The number of people missing in China’s Tibet after a Nepal mudslide disaster has risen to 558 including 260 foreign nationals, Chinese state broadcaster CCTV reported on Thursday, as authorities flagged more geological risk upstream.

A wall of mud and rock on Wednesday collapsed into a river near Gyirong at the border between the Tibet region and Nepal, triggering a flash flood that killed scores of people downstream in Nepal, left hundreds missing and washed away houses, roads and power projects.

China confirmed an official death toll of three on the Tibetan side of the border, CCTV reported. Surrounding villages within danger zones have been evacuated and two villagers have been rescued, it said without elaborating.

Authorities have identified risk from a dammed lake upstream from the Himalayan border crossing that could complicate rescue efforts, CCTV reported.

China’s Ministry of Water Resources has increased monitoring and assessment of the lake, at...