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

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.

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.

Millions continued to throng the site even as police urged them to avoid the area. Deadly stampedes are relatively common around Indian religious festivals, where large crowds gather in small areas.

Indian opposition leader Rahul Gandhi condemned organisers for "mismanagement" and a "focus on VIP movement" which he blamed for the deaths. Others, including Prayagraj local Rekha Verma, pointed the finger at heavy-handed tactics by "rude and abusive" police officers to keep immense throngs of devotees in line.

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.