Former police constable-turned-preacher Bhole Baba built an immense following among poor and marginalised Indians before his latest sermon ended in a stampede that killed 121 of his followers.

India is home to innumerable religious gurus or "godmen", whose devotees beseech them for miracles and donate money and possessions as a token of loyalty.

Baba, whose current whereabouts are unknown, was barely known to the wider Indian public before Tuesday's disaster.

But in his native state of Uttar Pradesh, he had cultivated a large audience of worshippers and his prayer meetings received thousands of views on social media.

"If you distribute flowers, you will receive a garland in return," he said during one sermon uploaded to YouTube two years ago, which focused on the virtues of kindness.

Past sermons show Baba dressed entirely in white, sitting on an ornate chair on a dais while addressing huge crowds of devotees, the vast majority of whom were women.

More than 250,000 people attended Tuesday's prayer meeting he staged near the northern city of Hathras, according to a police report.

- 'Don't do wrong' -

Very little is known about the early life of Baba, who was named Suraj Pal at birth but adopted his current moniker after devoting his life to spiritual instruction.

He was born in Uttar Pradesh to a farming family and served as a police officer in Agra, home to the Taj Mahal, before taking early retirement in the 1990s and pursuing his current calling, the Indian Express reported.

Baba's following was largely drawn from poor and socially disenfranchised caste groups including the Jatavs, who number in the tens of millions in the state.

The Jatavs belong to the bottom rungs of India's millennia-old caste hierarchy that divides Hindus by function and social standing. By virtue of their numbers, they are an important political bloc in Uttar Pradesh.

Baba helmed a monastery in the city of Mainpuri, not far from the site of Tuesday's stampede, where his weekly sermons reportedly drew thousands of people, predominantly women.

Ram Sanai, a 65-year-old devotee present at Tuesday's sermon, told AFP that part of Baba's appeal came from his admonitions against excessive alcohol consumption and advice for women facing domestic violence.

"All he says is don't steal, don't do wrong and stay honest," she said.

"Those who attend his events say they have then ended all negativity and problems at home."