The United Nations’ top official in Nepal has issued an emotional appeal for international aid, warning that survivors of the catastrophic Himalayan flooding last month saw their lives transformed “in one to two minutes”.

The UN Resident Coordinator, Lila Pieters Yahia, said communities along the China-Nepal border were struggling to comprehend the scale of devastation after torrential floods on August 26 tore through mountain districts, destroying roads, bridges and hydropower dams.

“You lose your home, you lose your livelihood, you lose your loved one and you lose the breadwinner of your family,” she told the AFP news agency in Kathmandu. “And you know, this happened in one to two minutes.”

At least 1,384 people were killed and more than 5,500 others remain missing in Nepal and the Tibet region of China. Among the missing are more than 800 foreigners from at least 34 countries, including tourists and pilgrims.

Many communities near the epicentre remain cut off, with roads washed away and journeys that once took hours now stretching into days. The UN, working with Nepal’s government, has launched a $50m appeal to support more than 84,000 people affected.

The UN’s Pieters Yahia warned of the risk of cholera and other communicable diseases, citing the deaths of 5,000 cattle and urging urgent investment in sanitation, hygiene and protection for vulnerable women and girls.

“My plea to the international community is: this is the time to help Nepal,” she said. “We can’t leave them alone.”