Millions of Hindus are gathering in a northern Indian city for the Maha Kumbh festival, the world’s largest religious congregation.

According to the Indian government, some 400 million people were expected to attend the Maha Kumbh Mela, the most important religious event in Hinduism, held this year in Prayagraj from January 13 to February 26.

At least 30 people have been killed and many more were injured in a stampede at the world’s largest religious gathering in India, police said. The tragedy took place as millions of pilgrims rushed to dip in sacred waters during the Maha Kumbh festival in the north of the country.

At least 17 people were killed and many more injured in a stampede at India's Maha Kumbh festival, the world's largest religious gathering, a doctor at a government hospital said, as tens of thousands of pilgrims rushed to dip in sacred river waters during the Hindu event.

It was not immediately clear what triggered the panic at the festival where devotees from across India had congregated to bathe at the confluence of the Ganges, the Yamuna and the mythical Saraswati rivers.

After dozens of people were killed in a crowd crush at the world's largest religious gathering, questions have been raised about security and crowd control at massive events in India.

People were trampled as pilgrims at the Maha Kumbh Mela, one of the world’s biggest gatherings, gathered at the confluence of two sacred rivers, officials said.

A senior police officer said at least 30 people died as a crowd panicked at the Hindu Kumbh Mela mega-festival in the northern city of Prayagraj.