KATHMANDU — Nepal's government declared a period of national mourning on Friday as the death toll from this week's Himalayan flash floods surpassed 1,500, the Home Ministry confirmed, with hundreds of people still unaccounted for near the Chinese border.

The floods, triggered by intense monsoon rainfall and glacial melt, devastated districts along the Nepal-China frontier. The Home Ministry said search and rescue operations were being scaled back in the worst-hit areas as the chance of finding survivors diminished.

Across the border in China's Tibet Autonomous Region, authorities maintained a toll of 43 dead with more than 500 people still missing.

The National Disaster Risk Reduction and Management Authority said thousands of families had been displaced, with washed-out roads and destroyed bridges hampering the delivery of aid to remote villages. Helicopters operated by the Nepal Army airlifted stranded residents and supplies to areas cut off by landslides.

The Prime Minister and senior government officials in Kathmandu pledged emergency relief funds and appealed for international assistance. The United Nations and the International Federation of Red Cross and Red Crescent Societies said they were mobilising support, while scientists linked the scale of the disaster to accelerating glacial melt across the Hindu Kush Himalaya.

The disaster ranks among the deadliest in Nepal's recent history, renewing scrutiny of the country's vulnerability to climate-driven extreme weather and the risk posed by unstable glacial lakes upstream.