A massive transfer of wealth is gaining speed, as billionaires are increasingly padding their vast fortunes with inheritance rather than entrepreneurship, a study by Swiss banking giant UBS showed Thursday.

Over recent decades, the number of billionaires has ballooned, with surging entrepreneurial activity within tech and other areas ushering fresh members into the super-wealthy club.

But in its ninth annual report on the world's billionaires, UBS noted a significant shift in the way such fortunes are being made and expanded.

"The heirs to billionaires are gaining prominence," Benjamin Cavalli, head of strategic clients at UBS Global Wealth Management, said in the foreword to the report.

"This year's report found that the majority of billionaires that accumulated wealth in the last year, did so through inheritance as opposed to entrepreneurship," he added in a statement.

"This is a theme we expect to see more of over the next 20 years, as more than 1,000 billionaires pass an estimated $5.2 trillion to their children."

That forecast, UBS said, was based on the estimated accumulated wealth of today's billionaires who are over the age of 70.

"After the surge in entrepreneurial activity witnessed over the past few decades, many business founders are now ageing and passing their wealth to the next generation," the study said.

The study indicated that there were 2,544 billionaires in the world by April this year, with their ranks swelling by seven percent in the preceding year.

After seeing their combined fortunes shrink the previous year, billionaire wealth grew by nine percent between April 2022 and April 2023 to $12 trillion, the study found.

The new billionaires included 53 heirs, whose accumulated inheritance amounted to $150.8 billion, exceeding the $140.7 billion joint fortunes of the 84 new self-made billionaires on the list, it said.

UBS attributed this shift in part to a subdued market for initial public offerings through 2022 and into 2023, limiting the opportunities for entrepreneurs to monetise the values of their businesses.