Millions of Hindus dipped into the frigid waters of three converging rivers in India Wednesday morning, marking the beginning of a 42-day bathing festival.

The pilgrims say the river water in the northern city of Allahabad is holy and has the power to wash away sin and stop the endless cycle of reincarnation.

Hindu devotees pray after taking a holy dip during the Ardh Kumbh Mela festival in Allahabad, India, on Wednesday.
(Rajesh Kumar Singh/ Associated Press)

Upwards of 70 million Hindus from across India and around the world are expected to gather in the city during the festival, chanting religious hymns as they bathe in the waters of the Ganges, Yamuna and Saraswati rivers.

Some say it is the largest gathering of people in the world.

"Initially I felt some cold but one dip and the cold was gone," pilgrim Ram Vir Upadhaya said Wednesday morning, a day marked by chilly winds, fog and temperatures of 6 C.

To prepare for the masses, the government has erected 50,000 tents and 25,000 toilets along an 80-kilometre stretch of the Ganges River.

Nearly 50,000 police officers are patrolling the area to prevent stampedes and watch for potential terrorist attacks.

"We have divided the whole area into different zones and in each zone we have provided an anti-sabotage check team and a bomb disposal squad," said police official Rajeev Sabharwal.

The event is costing the government an estimated $180 million.

The festival, called Ardh Kumbh Mela, occurs every six years. A larger bathing and pilgrimage festival, the Kumbh Mela, occurs every 12 years.

During Ardh Kumbh Mela, only six of 42 days are considered main bathing days. They are chosen based on the alignment of the stars.

Wednesday was one of the bathing days. An estimated three million people had dipped in the water in the first six hours of the morning, starting before dawn. Hindu saints, naked and smeared in ash, led the way.

With files from the Associated Press