By Zubair Ahmed BBC News, Mumbai

The conversion is expected to be the largest in modern times

Thousands of tribal and Dalit Hindus in India are to embrace the Buddhist faith at a huge gathering in Mumbai.

The ceremony, which may be presided over by Tibet's exiled leader, the Dalai Lama, is billed as the largest religious conversion in modern India.

The converts hope to escape the rigid caste system in which their status is the lowest.

Right-wing Hindus have often opposed conversion, pushing some Indian states to restrict legal changes of faith.

The organisers say the number of people to convert in Sunday's ceremony could go up to 100,000, easily the biggest mass conversion in India's recent history.

Conversion controversies

The Dalits, once known as Untouchables, hope the conversion will give them dignity and equal rights.

Commentators say that despite the reservation of jobs for the Dalit and tribal communities, their social status and economic conditions have not greatly improved.

They say that Dalits still face widespread prejudice and discrimination.

Conversion is a controversial subject in India, especially if it involves Hindus converting to Christianity or Islam.

Two weeks ago two Catholic priests were publicly beaten after being accused of trying to bring a group of local people into the Catholic faith.

But converting to Buddhism does not evoke much adverse reaction, as most hardline Hindu leaders believe Buddhism is an extension of Hinduism.

Even so, several Indian states, especially the ones governed by the right-wing Bharatiya Janata Party, BJP, have made laws severely restricting conversion.