KATHMANDU — The United Nations warned yesterday of the immense challenge of reaching Nepal flood survivors, with destroyed roads forcing aid workers to consider using cargo drones and porters to reach isolated Himalayan communities.

More than 1,200 people have been killed and some 5,600 are missing on both sides of the China-Nepal border since the catastrophic glacial mountain collapse on August 26, according to tolls by both nations yesterday.

“It is just incredible — the magnitude of the disaster, the magnitude of the destruction,” UN Resident Coordinator Lila Pieters Yahia told reporters in Kathmandu.

More than 800 foreigners from at least 34 countries are among those missing, including tourists and pilgrims, in both Nepal and Tibet in China.

In Kathmandu, families of some of the missing foreigners said they were combing hospitals and morgues for any information.

“I feel desperate, it’s been so many days,” said 53-year-old US citizen Sanjeev Rai who flew to Nepal to look for his wife, one of around 75 Americans missing.

In China, photographs of missing people are being shared on social media by relatives hoping for news.

“Hurry up and come back, your parents miss you a lot, we need you,” one woman wrote on a popular platform, posting an image of her relative, a police officer, and his wife.

Beijing keeps tight control over media access and information, and foreign journalists are restricted from reporting in Tibet.