MUMBAI (BLOOMBERG) – In June, Indian billionaire Mukesh Ambani and his aides ran into an unexpected dilemma when debating where to train the dealmaking lens of his empire next.

Mr Ambani’s Reliance Industries was contemplating buying a foreign telecommunications giant, when word reached them that Gautam Adani – who had overtaken Mr Ambani as Asia’s richest man a few months earlier – was planning to bid in the first big sale of 5G airwaves in India, according to people familiar with the matter.

Mr Ambani’s Reliance Jio Infocomm is the top player in India’s mobile market, while the Adani Group doesn’t even have a licence to offer wireless telecommunications services. But the very idea that he might be circling ground so core to Mr Ambani’s ambitions put the tycoon’s camp on high alert, according to the people.

One set of aides advised Mr Ambani to pursue the overseas target and diversify beyond the Indian market, while another counseled conserving funds to fend off any challenge on the home turf, according to people familiar with the discussions.

Mr Ambani, worth US$87 billion (S$120 billion), ultimately never bid for the foreign firm, partly, the people said, because he decided it would be more astute to retain financial firepower in case of a challenge from Mr Adani, who has seen his net worth surge more than anyone else in the world this year – to US$115 billion, based on data from the Bloomberg Billionaires Index.

After peacefully expanding in their respective domains for over two decades, Asia’s two richest men are increasingly treading the same ground, as Mr Adani in particular sets his sights beyond his traditional areas of focus.

That’s setting the stage for a clash with widening implications both beyond India’s borders, as well as at home as the US$3.2 trillion economy embraces the digital era, triggering a race for riches beyond the commodity-led sectors where Mr Ambani and Mr Adani made their first fortunes. The opportunities emerging – from e-commerce, to data streaming and storage – are reminiscent of the US’s 19th century economic boom, which fueled the rise of billionaire dynasties like the Carnegies, Vanderbilts and Rockefellers.

The two Indian families are similarly hungry for growth and that means they’re inevitably going to run into each other, said Arun Kejriwal, founder Mumbai investment advisory firm KRIS.

“Mr Ambanis and Mr Adanis will cooperate, co-exist and compete,” he said. “And finally, the fittest will thrive.”

In a public statement on July 9, the Adani Group said that it has no intention of entering the consumer mobile space currently dominated by Mr Ambani, and will only use any airwaves purchased at the government auction to create “private network solutions,” and for enhancing cybersecurity at its airports and ports.

Despite such commentary, speculation is rife that he might eventually venture into offering wireless services for consumers.

For decades, Mr Adani’s business were focused on sectors like ports, coal mining and shipping, areas that Mr Ambani stayed clear of amid its own heavy investments in oil. But over the past year, that’s changed dramatically.

In March, the Adani Group was said to be exploring potential partnerships in Saudi Arabia, including the possibility of buying into its mammoth oil exporter. A few months before that, Reliance – which still gets a majority of its revenue from businesses related to crude oil – scrapped a plan to sell a 20 per cent stake in its energy unit to Aramco.