Some 5,000 Dalits -- those at the bottom of the ancient religious hierarchy who were once known as untouchables -- converted to Buddhism in Mumbai, state capital of Maharashtra in western India, a Dalit group said.

"We estimate that close to 5,000 Dalits have chosen the path towards Buddhism by the end of the day," said Shravan Gaikwad, representative of the Samatha Sainik Dal, a Dalit group.

Large-scale Dalit conversions take place periodically in India, with close to 10,000 changing faith in October to mark the 50th anniversary of the conversion of their deceased political leader Bhimrao Ramji Ambedkar.

Ambedkar, a low-caste Hindu who rose to become a distinguished jurist and played a key role in drafting India's constitution, galvanised Dalits with his public rejection of caste and Hinduism itself.

Sunday's conversion came just two weeks after a Dalit woman was sworn in as chief minister of India's largest state in an unexpected majority win that some saw as a sign of how far the group has come.

But many Dalits say they still face severe discrimination and the conversions are a way to make a fresh start, as well as to draw attention to their plight.