The disaster struck early Wednesday near the Rasuwagadhi border crossing in Nepal's Rasuwa district, sending a torrent of mud, rocks and water downstream and sweeping away homes, vehicles, roads and other infrastructure.
Nepalese authorities said rescue teams had recovered 95 bodies, while dozens of people were injured and hundreds remained missing. At least 341 foreign travellers were reported missing, including more than 100 Indians, three US citizens and 12 British nationals.
Eight South Korean nationals working at a hydropower project were also reported missing.
Authorities have warned of the possibility of further flooding, with a blockage still lodged upstream. Residents living along the Bhote Koshi River were urged to move to higher ground.
The exact cause of the disaster remains unclear. Nepal's foreign minister initially said an earthquake may have triggered an avalanche and caused the flooding.
However, satellite analysis indicated that a landslide of snow and rock may have triggered a debris-filled flood in the Lhende River, about 20 kilometres northeast of the Rasuwagadhi border crossing.
The German Research Centre for Geosciences recorded a magnitude 4.4 earthquake around seven minutes before the incident captured on security footage.
Footage from the Chinese side of the border showed people fleeing moments before a torrent of rock, mud and water swept through the area, destroying buildings and vehicles.
On the Nepalese side, television footage showed collapsed homes, floating cars and a bridge being carried away by floodwaters.
Rescue operations have been hampered by continuing rainfall and difficult mountainous terrain. Helicopters have been unable to land in some of the affected areas, while officials warned that river levels could rise further.
The disaster also affected China's Gyirong border port in Tibet, where roads, communications and electricity links were damaged.
Chinese authorities deployed hundreds of rescuers, vehicles, search dogs and emergency equipment to the affected area. Officials said all roads leading to the border crossing had been severely damaged.
Chinese President Xi Jinping ordered an all-out effort to locate missing people and called for stronger monitoring and early-warning systems to prevent secondary disasters.
The flooding also prompted alerts in India's northern states of Uttar Pradesh and Bihar. Authorities in Bihar said they had evacuated around 5,000 people from six districts and planned to move up to 12,000 people to safety.
The Bhote Koshi River eventually flows into the Trishuli River and then into India as the Gandak River, raising concerns that the disaster could have wider consequences downstream.
