Vast crowds of Hindu pilgrims in India bathed in sacred waters as the Kumbh Mela festival opened on Monday, with organisers expecting 400 million people -- the world's largest gathering of humanity -- to assemble over six weeks.India is the world's most populous nation, with 1.4 billion people, and so is used to large crowds.

PRAYAGRAJ, India — Tens of thousands of naked Hindu ascetics and millions of pilgrims took dips in freezing water at the confluence of sacred rivers in northern India on Tuesday, in the first of a series of major baths in the Maha Kumbh festival, the largest religious congregation on Earth.

India's Maha Kumbh Mela, or Great Pitcher Festival, is set to be the world's largest gathering of humanity, with 400 million visitors expected at the six-week event that began this week in the northern city of Prayagraj.