Vast crowds of Hindu pilgrims in India began bathing in sacred waters on Monday as the Kumbh Mela festival opened, with organisers expecting 400 million people - the largest gathering of humanity.

Maha Kumbh Mela or Great Pitcher Festival begins in India on Monday, a Hindu sacred event that will be the world's largest gathering of humanity as it showcases religion, spirituality, tourism and crowd management.

The Maha Kumbh Mela, or the Great Pitcher Festival, will bring more than 400 million people to Prayagraj city in northern India over a period of six weeks starting Monday, making it the largest gathering of humanity in the world.

While the Kumbh Mela festival is ordinarly held every three years, rotating between several holy cities on the banks of these rivers, the Maha Kumbh Mela occurs only once every 12 years. Maha means “great”, and the event attracts the most devotees because it is considered the most auspicious and holy in the cycle.

On the banks of the Ganges River, the largest gathering of people in the world began in India’s Prayagraj, in northern Uttar Pradesh state.