The incident occurred in the Indian city of Indore when a concrete slab covering the roof of a stepwell in a temple complex gave way, crushing devotees who had gathered to celebrate the Hindu festival of Ram Navami on Thursday, officials said.
"The major cause of deaths could be drowning because the well was 60 feet deep and there was much water in it," Ilayaraja T, a top local government official, told Reuters.
Stepwells built hundreds of years ago are a common feature across India, many of them ornately decorated, with access to a body of water through stairs and niches.
"The stepwell was covered, but the slab covering it collapsed because of the crowd and extra load on it," Shivraj Singh Chouhan, Chief Minister of Madhya Pradesh, the state where Indore is located, told reporters late on Thursday.
Authorities were investigating the reason behind the collapse, Illayaraja said, adding that the last of the rescue operations were taking place to determine that there were no more people stranded in the debris.
Tens of army and rescue personnel worked through the day on Thursday to remove debris, using ropes and ladders to pull out people who had fallen into the well, Reuters reported.
There were an estimated 80 people in the complex when the accident happened, he said.
Stampedes and accidents in religious places are not uncommon in India, where a lack of crowd control and cramped spaces can spell danger.
Indian Prime Minister Narendra Modi expressed condolences and announced compensation for the dead and injured in the incident.
Videos and images of the rescue operation show a large, gaping hole in the ground under the temple, with people climbing up a ladder to the surface and authorities feeding ropes down. A metal wiring structure can be seen hanging off the edge, appearing to have given way; outside, anxious crowds gathered outside the temple, with authorities carrying out the injured on stretchers.