Crowds of mourners gathered in India's financial capital Mumbai on Thursday for the funeral of industrialist Ratan Tata, hailed as a "titan" who led one of the country's biggest conglomerates.

Tata, who died aged 86 on Wednesday, transformed the Tata Group into a sprawling international enterprise, with a portfolio ranging from software to sports cars.

His coffin, draped in an Indian flag, was flanked by a guard of honour, with a marching band of trumpets and drums accompanying the procession.

Mumbai has declared a day of mourning, with the funeral rites to take place on Thursday afternoon.

"A titan of Indian industry", The Hindu newspaper called him on its front-page. "India loses its crown jewel", the Hindustan Times wrote.

Tributes also poured in from fellow industrialists, with Asia's richest man Mukesh Ambani saying it was a "big loss, not just to the Tata group, but to every Indian".

Tata was born in Mumbai in 1937 into a family of Parsis -- a proud but dwindling community which played an outsized role in the city's business affairs under British rule.

He had intended to chart his own course in life as an architect after graduating from Cornell University in New York.