Five people have died in a stampede in the northern Indian city of Haridwar where hundreds of thousands have gathered for the Maha Kumbh festival.
Eyewitnesses said the stampede was triggered by clashes between Hindu holy men and devotees.
But an official said it followed a car accident. At least 15 people are reported to be injured.
Up to two million Hindus are likely to bathe in the Ganges on Wednesday - an auspicious day of the Kumbh festival.
The big Maha Kumbh festivals are held every 12 years, with lesser festivals held at stages in between.
The celebrations are among the largest religious gatherings in the world.
According to eyewitnesses, the incident took place near the Birla bridge.
It is not clear what caused the stampede.
Eyewitnesses said they followed a clash between the Naga holy men or naked hermits who came to take the "royal bath" or "shahi snan" and some devotees, the BBC Hindi's Shalini Joshi reports from Dehradun.
But an official said a car of a Naga holy man ran over two people, resulting in the stampede.
Some groups of holy men said they would boycott the bathing festival.
Officials say the situation is under control.
According to reports, hundreds of thousands of people have already taken a dip in the river since the early morning.
Hundreds of foreigners are also attending the festival.
In 1954, more than 800 pilgrims were killed in a stampede during the Kumbh festival in Allahabad.
Since then, authorities have been careful to deploy thousands of policemen and volunteers to ensure the festival passes off smoothly.
And although that mostly happens, at least 30 pilgrims were killed in a stampede during the Kumbh festival in Nasik in 2003.
And in 1986, 50 people died in a stampede at the Kumbh Mela in Haridwar.