Organisers of the world's biggest religious festival, which starts on the banks of the river Ganga on Monday, said they were ready for the tens of millions of pilgrims expected to attend.
The Kumbh Mela, which takes place on a 12-year cycle and will last 55 days, is being held in Allahabad where vast crowds of Hindus have already gathered ahead of the first mass bathing in the sacred river on Monday.
The organisation of the festival requires a monumental effort, but officials said everything was in place for a safe and successful event.
"All arrangements have been made to ensure that on this auspicious occasion the bathing can take place in a smooth and acceptable fashion," chief organiser Mani Prasad Mishra told AFP on Sunday.
Top Uttar Pradesh state police officer Arun Kumar said the biggest concern was crowd control and the 12,000 officers on duty would be monitoring to guard against stampedes -- a frequent and deadly occurrence at Indian religious festivals.
"We will be measuring the pressures in the crowd, with officers on the ground and we have also put in watchtowers and will monitor the entry points," Kumar, who is in charge of law and order, told AFP.
"We are totally prepared to handle this Mela."
Ahead of the Kumbh Mela, organisers set up 35,000 toilets, 14 medical centres, 22,000 street lights, 150 kilometres (93 miles) of temporary roads, 18 bridges, and new sewage facilities.
An estimated 100 million people are expected, with as many as 20 million anticipated on the most auspicious bathing day, February 15, organisers say.
Thousands streamed into Allahabad on Sunday, swarming off special buses and trains transporting Indians from all over the country who believe a dip in the Ganges cleanses them of their sins.
At the numerous bathing locations, where the Ganges is joined by the Yamuna river, which flows through New Delhi, many opted for an early bath before the crush on Monday.
Men in underpants and women wearing saris splashed into the fast-flowing and freezing water, often repeating prayers and releasing flower tributes.
The Kumbh Mela has its origins in Hindu mythology which tells how a few drops of the nectar of immortality fell on the four locations that host the festival every three years -- Allahabad, Nasik, Ujjain and Haridwar.
The Kumbh Mela in Allahabad takes place every 12 years and is the largest of the four.