Google is to buy a $4.5-billion stake in Reliance's digital unit, the head of the Indian conglomerate said Wednesday as global tech giants race to grab a share of the massive e-commerce market.

"We are delighted to welcome a household name in India and worldwide, Google, and have signed a binding partnership and investment agreement," which will give the Silicon Valley firm a 7.7-percent stake in Jio Platforms, Mukesh Ambani told shareholders at the oil-to-telecom behemoth's annual meeting.

Major players including Facebook, Intel and others have already ploughed some $15 billion into Jio Platforms this year, as Ambani -- India's richest man -- seeks to take on US giants Amazon and Walmart in India's growing online retail sector.