Mimi Lau reports on the developing flood disaster in the central Chinese city of Zhengzhou following record-smashing rains which have pushed the Yellow River to extreme heights, displacing hundreds of thousands of people and threatening nearby dams. Hear first-hand accounts of people trapped in subway trains as flood waters filled the tunnels, and analysis from Beijing-based reporter Echo Xie on how these floods differ from last year's floods on the Yangtze River.