In pictures: Kumbh Mela gets under way

Naga sadhus run in to bathe in the waters of the holy Ganges river during the auspicious bathing day of Makar Sankranti of the Maha Kumbh Mela on 14 January 2013 in Allahabad, India

India's Kumbh Mela is under way. Major versions of the festival are held every 12 years and this is thought to be the world's largest gathering of humanity.

Devotees arrive for a dip at Sangam, the confluence of the Rivers Ganges, Yamuna and mythical Saraswati, on the first day of the Kumbh Mela

Millions of people arrived for the first day of the festival, in Allahabad, which is expected to attract more than 100 million people over the next 55 days.

Hindu devotees pray in the waters of the Sangham or the confluence of the the Yamuna and Ganges rivers during the Kumbh Mela in Allahabad

Hindus believe a dip at the confluence of the Ganges and Yamuna rivers in Allahabad, called Sangam, will cleanse sins and help bring salvation.

Naked Hindu holy men or Naga sadhus leave from their camp for a dip at Sangam, the confluence of the Rivers Ganges, Yamuna and mythical Saraswati on the first day of the Kumbh Mela

The festival started at dawn, led by naked ash-smeared Hindu holy men - Naga sadhus - with marigold garlands around their necks.

Sadhus, run into the water at Sangam, the confluence of the rivers Ganges, Yamuna and mythical Saraswati, during the royal bath on Makar Sankranti at the start of the Maha Kumbh Mela in Allahabad, India

The sadhus arrived in a colourful procession and sprinted into the chilly waters of the Sangam.

Hindu devotees bathe in the waters of the Ganges river during the auspicious royal bathing day of Makar Sankranti, the start of the Maha Kumbh Mela, in Allahabad, India, 14 January 2013

Ordinary men and women followed the sadhus into the water - many had come from all parts of this vast country to take part.

Hindu devotees bathe in the waters of the Ganges in Allahabad, India, 14 January 2013

Millions of pilgrims are expected to flock to the holy river during the next eight weeks - at its peak, authorities expect nearly 30 million people to be on the site.

Millions of Hindu devotees gather early in the morning at Sangam, the confluence of the Rivers Ganges, Yamuna and mythical Saraswati, on the first day of the Kumbh Mela.

Allahabad has been preparing for the festival for months, and 14 temporary hospitals and 40,000 toilets have been built to cope with the millions of pilgrims.

An Indian Hindu boy is held by his father as they go for a dip at Sangam, the confluence of the rivers Ganges, Yamuna and mythical Saraswati, during the royal bath on Makar Sankranti at the start of the Kumbh Mela

Teams are managing crowds on the river bank, encouraging pilgrims who have finished bathing to move away and make space for others.

Mounted policemen patrol during the first grand bath in Allahabad, 14 January 2013

Several squads of police on horseback regulated the flow of pilgrims to and from the waters. Some 50,000 have been deployed to keep order during the festival.

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