Indian billionaire Mukesh Ambani on Monday announced an investment of $25 billion to launch 5G networks in India, aiming to strengthen his grip on one of the world's fastest-growing smartphone markets.

In his annual speech delivered virtually to shareholders of Reliance Industries -- India's most valuable company -- Asia's second-richest person said he believes "digital freedom is the birthright of every Indian".

Ambani's multi-billion-dollar empire was built on oil and petrochemicals, but he has diversified into new areas including telecoms, retail and renewable energy in recent years.

The launch of telecom arm Jio -- offering ultra-cheap data at high speeds -- in 2016 sparked a brutal price war, forcing competitors into years of losses.

Earlier this month, Jio swept up more than a third of the available spectrum in India's first-ever 5G airwave auction, bidding 881 billion rupees ($11 billion).

Announcing an investment of two trillion rupees ($25 billion), Ambani said Jio will launch 5G services in major cities including Delhi, Mumbai, Kolkata and Chennai in time for the Indian festival of Diwali in late October.

A pan-India roll-out will follow, Ambani said, with an aim to cover every district in the country by December 2023 -- an area of 3.3 million square kilometres.

"We are committed to make India the largest data-powered economy in the world, even ahead of China and the United States. Jio 5G will be the world's largest and most advanced 5G network," Ambani said.

Global tech giants such as Google, Facebook owner Meta, Intel and Qualcomm have invested billions of dollars into Reliance's digital unit Jio Platforms in recent years.

A newly-launched collaboration between Meta and Jio will allow users to shop for groceries via instant messaging app WhatsApp, Ambani said.

"This is our first-ever end-to-end shopping experience on WhatsApp -- people can now buy groceries from JioMart right in a chat," Facebook founder and Meta CEO Mark Zuckerberg said in a Facebook post.

In June, Ambani's 30-year-old son Akash was appointed chairman of Jio Infocomm, a subsidiary of Jio Platforms, sparking speculation about succession planning.

Ambani stopped short of announcing leadership changes at Monday's AGM, instead asking shareholders to extend their blessings to his three children Isha, Akash and Anant.

The 65-year-old business tycoon was until this year Asia's richest person but was unseated by fellow Indian billionaire Gautam Adani.

India is home to the second-highest number of smartphone users after China.

The country's long-delayed 5G push comes as the world's sixth-largest economy tries to bridge a technology gap with rivals such as South Korea, China and the United States.

Shares in Reliance Industries closed 0.69 percent lower in Mumbai following the announcements.