Millions of Hindu devotees are gathering in northern India for the Magh Mela -- one of the world's biggest religious festivals involving ritual bathing in the holy waters of the Ganges river.

An estimated 10 million Hindus descend on the city of Allahabad every January for the festival staged at the sacred meeting point of the Ganges, Yamuna and mythical Saraswati rivers.

The 45-day Mela is currently underway, with pilgrims camping across Allahabad and joining the colourful throngs for dips in the venerated waters.

Among them is Shiv Yogi Moni Swami, a holy man smeared in sandalwood paste, carrying a trident and clad in nothing more than beads and a leopard-print wrap around his waist.

Swami demonstrates his devotion not by walking to the confluence of the rivers known as the Sangam but by rolling the roughly one-kilometre distance from his tent to the waters.

It is not an easy task, with his body collecting dust and grime before he arrives at the confluence where he submerges himself fully.

The act "purifies the soul and washes away all sins", he told AFP, after scattering rose petals to the rising sun and performing his ablutions.

"As we bathe on this holy day in the Ganges we are praying not only for peace of our soul but for the welfare of the whole world," Swami added.

Fellow pilgrims, impressed by his piety and fortitude, bow to touch his feet and take blessings.

Some even lie prostrate before him as he passes in a sign of reverence.

Many Indians believe that holy men like Swami possess mystical powers and are capable of curing all manner of illnesses.

For the duration of the Mela, Swami says he eats just one simple meal of fruit a day, apparently enough to sustain him through a busy schedule of chanting prayers and performing yagna, a centuries-old Hindu fire ritual.

"I believe that if you all bow before the Ganges you will be blessed with eternal peace and happiness," he said, explaining his devotion to the holiest river in Hinduism.

"She (Ganges) is just like a mother. Just like a mother is kind to all, be it a Christian, Buddhist, Muslim or a Jain, the Ganges is all encompassing."

The annual ritual has been held in Allahabad for centuries and is a smaller version of the Kumbh Mela, a gigantic event attended by tens of millions that UNESCO describes as the largest peaceful gathering of pilgrims on earth.