Naked Hindu ascetics and pilgrims are taking holy dips in sacred rivers in the first major bathing day of the Maha Kumbh festival, which is the largest religious congregation on Earth.

Scores of naked Hindu ascetics smeared in holy ash charged into the water of holy rivers in northern India on Tuesday, dreadlocks flying, during the first 'royal bath' of the Maha Kumbh Mela, or Great Pitcher Festival.

Over about the next six weeks, Hindu pilgrims will gather at the confluence of three sacred rivers where they will take part in elaborate rituals.