Millions of Hindu devotees will take a holy dip in the Ganges River on Monday on one of the six most auspicious days to bathe during Kumbh Mela - the world’s largest religious festival.

More than 18 million pilgrims - led by naked, ash-smeared ascetics - entered the grounds last week as the festival began.

During the eight-week gathering at Prayagraj, in the northern state of Uttar Pradesh, up to 150 million people, including a million foreign visitors, are expected to bathe at the confluence of the Ganges, the Yamuna, and a mythical third river, the Saraswati.

Prime Minister Narendra Modi's Bharatiya Janata Party, which governs the state, sees a successful festival as a way to burnish its credentials as a defender of the Hindu faith. Giant cardboard cutouts of Modi, who faces a tough test in a general election due by May, have adorned the sacred site.

For the first time at the Kumbh Mela, a transgender ashram known as the Kinnar Akhara and led by rights LGBTQ activist Lakshmi Narayan Tripathi from Mumbai, joined the holy bathing. Tripathi, a tattooed transgender leader and a former reality TV star, has become an unlikely icon at the festival.

India legalised gay sex in September, but the LGBTQ community still faces prejudice in the deeply religious country.

Members of the Kinnar Akhara received a police escort to the bathing site, where Tripathi last Tuesday plunged into the waters fully clothed to the cheers of her followers.

Tripathi has courted controversy with support for the building of a temple dedicated to Ram on the site of a former mosque in Ayodhya, which was demolished by hardline Hindus in 1992, leading to riots in which thousands died.

The Kumbh Mela festival has its roots in a Hindu tradition that says the God Vishnu wrested a golden pot containing the nectar of immortality from demons.

In a 12-day fight for possession, four drops fell to Earth, in the cities of Prayagraj, Haridwar, Ujjain and Nasik, which now share the Kumbhs.