The stampede happened as hundreds of devotees of Indian guru Jai Gurudev gathered in Varanasi, a Hindu holy town in Uttar Pradesh state, a place known for its temples.
Police officer S.K. Bhagat said organizers expected about 3,000 people to attend the ceremony, but more than 70,000 turned out.
Police started turning back people from an overcrowded bridge, triggering a rumor among the devotees that the bridge had collapsed and causing throngs of people to run for safety.
Television footage showed colorful clothing piled up with police officers trying to clear debris.
"There was a lot of chaos. All of us were pushed and shoved. Many people have died including my mother," a witness told reporters as rescue efforts were underway.
Several people were injured, some seriously. They were taken to local hospitals while authorities rushed to the site to assess the situation.