Millions of Hindu pilgrims are gathering in India to bathe in sacred waters for the six-week-long Kumbh Mela festival -- from the very old to babies, cave-dwelling monks to science teachers.

The millennia-old Kumbh Mela, a show of religious piety and ritual bathing -- and a logistical challenge of staggering proportions -- is held in the northern city of Prayagraj in Uttar Pradesh state.

Organisers are expecting 400 million people at the festival, which began on Monday and runs until February 26.

Here are snapshots of some of those taking part in the world's largest gathering of humanity.

Studying artificial intelligence engineering at a private college in New Delhi, 18-year-old Rishabh Kumar Singh lied to his teacher to attend the festival, saying he was unwell.

But Singh said his mother approved of the trip -- and got her husband to sponsor it.

"I got my devotional streak from her," he said.

"As a child, she would take me along to all kinds of religious ceremonies."

Singh took an overnight train from the capital to arrive in time for the first day of........

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