The world's richest people became a little less well off last year, according to a report by UBS and PricewaterhouseCoopers (PwC), as geopolitical turmoil and volatile equity markets reduced the wealth of billionaires for the first time since 2015.

Billionaires' wealth fell by 4.3 per cent globally to $8.5 trillion US last year, the joint UBS-PwC report found, with a sharp decline in China, including Hong Kong, and the Asia-Pacific region more broadly.

Private wealth in Hong Kong fell four per cent in 2018 to $319.8 billion US, the report showed, with months of anti-government protests in the Chinese-ruled city and an economic recession clouding the outlook this year.

Some Hong Kong tycoons have begun moving personal wealth offshore, Reuters reported in June, as concerns deepen over the protests.

"We haven't seen any significant outflows; we have been tracking some of these numbers on a regular basis," said Amy Lo, UBS's co-head of Asia Pacific wealth management. "Our clients have been diversifying all along; it's not in the last one year."

Private banks, including the world's largest wealth manager UBS, have felt the effects of U.S.-China trade tensions and global political uncertainties, as clients last year shied away from trading and taking on debt in favour of hoarding cash.

The net worth of China's richest dropped 12.8 per cent in dollar terms on the back of tumbling stock markets, a weaker local currency and a slowdown in growth, the report found, knocking dozens off the billionaires list.

Despite the drop, China still produces a new billionaire every two to 2.5 days, UBS's head of ultra-high net worth clients, Josef Stadler, said in the report released Friday.

Worldwide, the number of billionaires fell everywhere except in the Americas, where tech entrepreneurs continued to buoy the ranks of the United States' wealthiest.

"This report shows the resilience of the U.S. economy," where there were 749 billionaires at the end of 2018, said John Matthews, head of private wealth management and ultra-high net worth business for UBS in the U.S.

While a stock market recovery from a steep drop in late 2018 has helped wealth managers increase their assets, the world's richest families remain concerned about global affairs — from trade tensions and Brexit, to populism and climate change — and are keeping more of their money in cash.

"It is likely that billionaire wealth will go up again this year," said Simon Smiles, UBS's chief investment officer for ultra-wealthy clients, adding it would likely be a more muted increase than the wider financial market rally might suggest.