The largest religious gathering anywhere on earth gets underway on Tuesday, with tens of millions of Hindu pilgrims congregating to bathe in sacred rivers for the Kumbh Mela.

Organisers are expecting the enormous spiritual festival in Allahabad to attract more than 100 million devotees over the next 48 days, with seas of pilgrims camped by the riverside.

Naked, dread-locked holy men smeared in ash and sadhus clad in saffron robes wander the crowds, offering blessings to pilgrims who have travelled from every corner of India for the ritual dip.

Nearly 30,000 police have been deployed to oversee crowds for the huge undertaking and to prevent stampedes that have marred previous gatherings.

A tent city with restaurants, roads and marketplaces has sprung up along the river, with pilgrims camped out across a sprawling 45-square kilometre zone specially earmarked for the Kumbh.

The largest religious gathering anywhere on earth gets under way Tuesday, with tens of millions of Hindu pilgrims congregating to bathe in sacred rivers for the Kumbh Mela.

Organisers are expecting the enormous spiritual festival in Allahabad to attract more than 100 million devotees over the next 48 days, with seas of pilgrims camped by the riverside. The ancient city in Uttar Pradesh rises alongside the banks of the Ganges, Yamuna and mythical Saraswati rivers.

Naked, dread-locked holy men smeared in ash and sadhus clad in saffron robes wander the crowds, offering blessings to pilgrims who have travelled from every corner of India for the ritual dip. Nearly 30,000 police have been deployed to oversee crowds for the huge undertaking, and prevent stampedes that have marred previous gatherings. A tent city with restaurants, roads and marketplaces has sprung up along the river, with pilgrims camped out across a sprawling 45-square kilometre zone specially earmarked for the Kumbh.