The stampede happened in a village in Hathras district in Uttar Pradesh, about 200 kilometres southeast of the capital New Delhi. Authorities said thousands had gathered in sweltering late afternoon temperatures.
The stampede occurred when a crowd of devotees started pushing towards the stage after the event to touch the preacher, who was coming down, said Yogi Adityanath, chief minister of Uttar Pradesh, India's most populous state.
While the cause was not immediately clear, Hathras district administrator Ashish Kumar suggested it may have been "due to overcrowding at the time when people were trying to leave the venue".
Another senior state official, Chaitra V, told broadcaster India Today that people may have lost their footing as they sought water in the heat.
Police said they had launched an investigation and promised action against anyone found to be responsible, adding that the gathering may have been larger than had been permitted.
With AAP.