A stampede injured dozens of people early Wednesday as tens of thousands of Hindus rushed to take a holy bath in the river at themassive Maha Kumbh festival in northern India, local media reported.

It was not immediately clear what triggered the panic at the festival where devotees from across India had congregated in the city of Prayagraj to bathe at the confluence of the Ganges, the Yamuna and the mythical Saraswati rivers. News agency Press Trust of India cited authorities who said injured people were sent to a hospital.

The Maha Kumbh festival, held every 12 years, started on Jan. 13 and is the world’s largest religious gathering. Authorities expect more than 400 million people to throng the pilgrimage site in total over the next six weeks.

To accommodate tens of thousands of holy men, pilgrims and tourists visiting the festival, authorities have built a sprawling tent city on the riverbanks. It’s equipped with 3,000 kitchens and 150,000 toilets and also has roads, electricity and water, communication towers and 11 hospitals.

About 50,000 security personnel are stationed in the city to maintain law and order and manage crowds. Stampedesare relatively commonaround Indian religious festivals, where large crowds gather in small areas.