Nearly 15 million Hindus, six times the number expected, took a dip in freezing waters seeking absolution of their sins on Monday, the first day of India's festival that could draw the world's largest single gathering of humanity.

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.

Over the coming 45 days, an estimated 400 million Hindus are expected to come together for Maha Kumbh Mela. The festival is held every 12 years but the "Maha" or grand Kumbh Mela takes place only every 144 years, "marking the 12th Kumbh Mela and a special celestial alignment of the sun, moon and Jupiter", said The Guardian.

Swami Bhupender Giri, centre, Naga Sadhu of Niranjani Akhara, arrives for ritualistic dip at Sangam, the confluence of the Rivers Ganges, Yamuna and mythical Saraswati on one of the most auspicious day Makar Sankranti,

India's Mahakumbh Mela, which is the world's largest religious gathering, entered its second day. Over the next six weeks, 400 million visitors are expected to attend the festival. Thousands of religious leaders and pilgrims could be seen charging into the icy waters in a ritual they believe will cleanse them of sin and help them achieve salvation.

Millions of Hindu pilgrims gathered on Tuesday at the confluence of the Ganges, Yamuna and Sarasvati rivers to take part in the first holy bath of the Kumbh Mela, the world's largest religious gathering.