The incident took place at a satsang (a Hindu religious event) in Hathras district in Uttar Pradesh state.
The victims, including a large number of women and some children, are still being identified.
Survivors have described how the disaster unfolded as they tried to leave the event in Mughalgarhi village.
It is not yet clear what led to the crush. Witnesses said the exit was too narrow and when people were leaving, a fierce dust storm led to confusion and panic, causing many people to become trampled.
An eyewitness, who asked to remain anonymous, told the BBC everything was "going fine", until "all of a sudden I heard screams and before I knew it, people were falling on each other".
"When the sermon finished, everyone started running out," a woman named only as Shakuntala told the Press Trust of India news agency.
"People fell in a drain by the road. They started falling one on top of the other and got crushed to death."
Umesh Kumar Tripathi, chief medical officer from the neighbouring district of Etah, told reporters the "stampede" had left at least three children dead.
A spokesperson for a senior police officer in Uttar Pradesh told the BBC it would "take hours to release the final tally".
Distressing images from the site are being circulated online. Some videos showed the injured being taken to hospitals in pick-up trucks, tuk tuks and even motorbikes.
A clip seen by the BBC showed several bodies left at the entrance of a local hospital as relatives screamed for help.
"Such a huge accident has happened but not a single senior officer is present here,” a relative in another video said. “Where is the administration?"
Mr Kumar said the venue had been overcrowded, adding that a high-level committee had been formed to investigate the incident.
"The primary focus of the administration is to provide all possible help to the injured and kin of the deceased," he said.
A video shared by news agency PTI showed the wounded being brought to a hospital for treatment.
"Procedure of post-mortem is under way and the matter is being investigated," official Satya Prakash in the neighbouring district of Etah said.
In Hathras, the screams of distraught family members can be heard in the local hospital.
Many people are trying to find their loved ones, many bodies are unclaimed.
There is a shortage of ambulances – each one is bringing two to three bodies. Hathras is filled with despair and pain.
Accidents are routinely reported at religious events in India, as huge crowds gather in tight spaces with little adherence to safety measures.
In 2018, around 60 people were killed after a train rammed into a crowd watching celebrations for Dusshera, a Hindu festival.
In 2013, a crush at a Hindu festival in the central state of Madhya Pradesh had killed 115 people.'Satsang' preacher Bhole Baba's lawyer AP Singh said the preacher is ready to cooperate with the state administration and the police probing Tuesday's stampede. "Some anti-social elements hatched a conspiracy,” he claimed.
'Mukhya sevadar' Devprakash Madhukar and other organisers are named as the accused in the FIR filed at the Sikandra Rau police station late on Tuesday. The preacher Jagat Guru Saakar Vishwahari Bhole Baba is not in the list.
The chief minister said the judicial probe team would include retired police and administration officials. “If this is not an accident, then whose conspiracy is this? All of this will be probed,” he told reporters during his visit to Hathras, where he met the injured.
At least two pleas were filed in courts on Wednesday over the tragedy.
An advocate filed a PIL in the Supreme Court seeking the appointment of a five-member expert committee under the supervision of a retired apex court judge to probe the incident. In the Allahabad High Court another PIL sought a probe by the Central Bureau of Investigation (CBI).
But Adityanath and the FIR appeared to give a clean chit to the local administration, seemingly laying the blame on the ‘sevadars' looking after the arrangements at the ‘satsang'.
The organisers tried to hide the actual number of people coming to the event by concealing evidence and throwing slippers and other belongings of the devotees in nearby fields, the FIR alleged.
The FIR said police and administration officials did everything possible with available resources and sent the injured to hospitals but the organisers and 'sevadars' did not cooperate.
According to the FIR and a preliminary report by the Sikandra Rau sub divisional magistrate, the stampede took place as the preacher left the venue.
People rushed towards him – apparently to have a 'darshan' and to collect some soil from the spot he had walked upon – and the 'sevadars' shoved them away. The SDM's report said many slipped while descending a slope next to the highway.
The CM said the "sevadars" should have taken the victims to hospital. People were dying and the sevadars fled, he claimed.
Asked why the preacher was not named in the FIR as an accused, Adityanath said, "Prima facie, the case has been filed against those who applied for permission for the event. Whoever is responsible for this will come under its purview."
The government has formed a special investigation team led by Agra's additional director general of police Anupam Kulshreshtha.
Asphyxia due to compression was the leading cause of death, a senior doctor at an Etah hospital said.
The FIR has been registered under Sections 105 (culpable homicide not amounting to murder), 110 (attempt to commit culpable homicide), 126 (2) (wrongful restraint), 223 (disobedience to order duly promulgated by the public servant), 238 (causing disappearance of evidence) of the Bharatiya Nyaya Sanhita, an official said.
A day after the tragedy, family members tried to come to terms with their loss.
Among them was 29-year-old Satyendra Yadav, a taxi driver from Delhi who lost his three-year-old son Rovin, affectionately called Chhota. He was in Hathras with his entire family, including his mother, wife and two children.
The anguished father, who performed Chhota's last rites on Tuesday night, said he doesn't remember much of what happened.
And Rajkumari Devi from Unnao said, "It's only the poor who meet this fate, not the rich."
Sitting in an ambulance beside the body of her sister-in-law Ruby, Rajkumari said she is worried about Ruby's five-year-old son who is missing. "We are yet to find him. More of our family members are on their way to Hathras."
Asked if she had any demands from the government, Rajkumari told PTI, "What do we say now? There's nothing (to ask for).”
