Several million Hindus jumped into the freezing waters of the River Ganges at 5am this morning as the world's biggest religious festival got under way.
Millions more are expected to arrive for the Kumbh Mela in the northern Indian town of Allahabad throughout the course of the day.
Devotees, who plunged into the water fully or partially clothed, believe that a dip in the sacred river will cleanse their sins.
The event began with bearded, naked and dreadlocked holy men, known as “sadhus”, running en masse into the water, while carrying swords and sticks and wearing little more than yellow garlands.
This was followed by a procession of naked ash-smeared men wading into the meeting point of the Ganges and Yamuna rivers.
Organisers estimate that around 100 million people will attend the festival over the next month-and-a-half.
The Kumbh Mela takes place every 12 years in Allahabad with smaller but similar events every three years in other locations around India.
Devesh Chaturvedi, an Allahabad administrator, said: "The biggest challenge for us is to ensure that we are able to provide an opportunity for each and every person to bathe on the auspicious days without any stampede."
A risk of stampede remains a concern for organisers after 45 attendees were crushed to death when the festival was held in the western Indian town of Nasik in 2003.
This year's organisers have put 12,000 police officers at designated check-points and have set up 14 medical centres, 150km (93 miles) of temporary roads, 18 bridges and a closed circuit camera system to ensure the event goes smoothly.
Organisers, who are also worried about potential environmental damage, have banned pilgrims from bringing plastic bags to the festival site and from using soap while bathing.
The danger of bathing in the heavily polluted Ganges is an additional concern for organisers who have opened upstream fresh water reservoirs in an attempt to dilute the dirty river water.
Kumbh Mela twas last hosted by Allahabad in 2001, when around 110 million pilgrims passed through without incident.
The festival takes its name from a Hindu belief that gods and demons fought over a pitcher, or "kumbh", of nectar that would give them immortality.
The myth says one of the gods ran off with the pot, spilling four drops of nectar: one on each of the festival’s host sites.