India's Hindu Kumbh Mela festival begins in Allahabad

Sadhus - Hindu holy men - play an important part in the festivities at Allahabad

Hundreds of thousands of people have been bathing at the confluence of the Ganges and Yamuna rivers at Allahabad in India, on the opening day of the Kumbh Mela festival.

Up to 10 million more pilgrims are set to do so by the end of the day.

The event, every 12 years, is billed as the biggest gathering on Earth. More than 100 million people are expected to attend the 55-day festival.

Hindus believe a festival dip will cleanse sins and help bring salvation.

In 2001, more than 40 million people gathered on the main bathing day of the festival, breaking a record for the biggest human gathering.

The Kumbh Mela has its origins in Hindu mythology - many believe that when gods and demons fought over a pitcher of nectar, a few drops fell in the cities of Allahabad, Nasik, Ujjain and Haridwar - the four places where the Kumbh festival has been held for centuries

Kumbh Mela in numbers

• Visitors: 80-100 million
• Number of days: 55
• Area: 20 sq km (4,932 acres)
• Drinking water: 80 million litres
• Toilets: 35,000
• Doctors: 243
• Police: 30,000

Most pilgrims drink a few drops of the Ganges water and many fill bottles to take home with them.

Authorities say they have taken steps to address the concerns.

Last week, companies along the banks of the Ganges and Yamuna were warned against discharging any pollutants into the waters.

Reservoirs upstream have been ordered to discharge fresh water into the rivers ahead of the six big bathing days, and the festival authorities have declared the Kumbh Mela area a plastic-free zone.

The Kumbh Mela, which is costing the authorities 11.5bn rupees ($210m; £130m) to organise, is expected to generate businesses of at least 120bn rupees, according to a report by industry association The Associated Chambers of Commerce and Industry (Assocham).

The report says that the festival is expected to draw over a million foreign tourists too.