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.

Hotel bookings in Prayagraj have increased nearly 10-fold from last year, while flight bookings to the city are up 65%, with tickets costing twice as much as last year on average.

While the Kumbh Mela festival is ordinarly held every three years, rotating between several holy cities on the banks of these rivers, the Maha Kumbh Mela occurs only once every 12 years. Maha means “great”, and the event attracts the most devotees because it is considered the most auspicious and holy in the cycle.

Over 6 crore devotees have participated in the worlds biggest religious congregation; over 3.5 crore on the occasion of Makar Sankranti on January 14.

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.

India began on Monday its Maha Kumbh Mela, or Great Pitcher Festival, which is expected to draw more than 400 million visitors to the northern city of Prayagraj over six weeks, making for the largest gathering of humanity in the world.