Millions of people have been driven from their homes by monsoon rains that caused an unexpected shift in direction of a major river in northern India.

Until last week, the Kosi, a tributary of the Ganges, curved westwards out of Nepal in a C-shape. But in the torrential rains that have hit the region, the river burst its banks and diverted southwards through the state of Bihar, into a channel it had followed 200 years previously.

Dozens of people have died and more than two million have been displaced in the floods.