Natural causes :

The Yangtze-Huai or China River Floods, which occurred in 1931, are considered to be the deadliest natural disaster ever recorded. While estimates are rough, it is believed that a minimum of one million people died, but this figure is likely closer to 3.7 million.

Primarily affecting the Yangtze, Huai and the Yellow River basins between July and November, the floods were caused by a combination of excessive rainfall, snowmelt and failing dikes which were installed to prevent floods.

The submersion of vast areas of land around these rivers displaced more than 25 million people, many of whom had their homes and livelihoods destroyed. Food shortages were severe and continuous outbreaks of disease killed millions.

The Chinese government and local authorities implemented large-scale emergency plans but the scale of disaster was just too large to be managed by their existing resources.