Indian tycoon Gautam Adani on Friday secured a majority stake in leading news broadcaster NDTV, finalising a hostile takeover that has sparked press freedom fears in the world's biggest democracy.

Adani, 60, is the world's third-richest person, with an estimated net worth of $130 billion and interests ranging from Australian coal mines to India's busiest ports.

He is also seen as a close acolyte of Hindu nationalist Prime Minister Narendra Modi, often publicly supporting his policies.

His business empire first began buying up NDTV shares in August, a move its founders Prannoy and Radhika Roy said had come without their involvement or consent.

But after months of negotiations, the Roy family agreed to sell most of their remaining equity, and the Adani Group said in a Friday stock market disclosure that its subsidiary RRPR had bought a 27.26 percent stake in the company.

The latest purchase gives Adani's conglomerate a 64.71 percent stake in NDTV, renowned for inviting government critics and its hard-hitting reporting in a TV news landscape dominated by pro-Modi coverage.

Adani has pledged to guarantee the channel's editorial independence but also told the Financial Times last month that journalists should acknowledge when the government was performing well.

"Independence means if government has done something wrong, you say it's wrong," Adani told the British broadsheet.

"But at the same time, you should have courage when the government is doing the right thing every day. You have to also say that."

Under Modi, India has slipped 10 places in the Reporters Without Borders global press freedom ranking and is now 150 out of 180 surveyed countries.

Critical reporters often find themselves behind bars and hounded on social media by supporters of Modi's ruling Bharatiya Janata Party (BJP).

Adani this year overtook fellow Indian Mukesh Ambani to become Asia's richest man, behind France's luxury goods mogul Bernard Arnault and Tesla boss Elon Musk.

But his group's growth into capital-intensive businesses has raised alarm, with analysts from Fitch Group's CreditSights warning in August that it was "deeply overleveraged".