ZURICH (Reuters) - Singapore and Hong Kong together will hold as much overseas wealth as Switzerland in four years' time, according to a study by Boston Consulting Group (BCG).

It underscores the boom in private wealth in the Asia-Pacific region as well as the impact on Switzerland from the clampdown on tax evasion after the financial crisis.

Banks in Switzerland stored US$2.4 trillion (S$3.3 trillion) in offshore riches in 2016, the highest in the world, BCG wrote in its annual global wealth report published on Tuesday (June 13). BCG expects this number to rise to US$2.8 trillion by 2021.

However, Singapore and Hong Kong together are on track to match Switzerland's expected 2021 total thanks to their proximity to Asia-Pacific's swelling population of millionaires and billionaires, BCG said.

In 2016, Singapore had US$1.2 trillion and Hong Kong US$800 billion in offshore wealth.

"Switzerland remained the largest offshore centre with a 24 per cent share," BCG wrote in its report, "but that share is projected to decline through 2021."

Major Swiss banks UBS and Credit Suisse have made major pushes to expand in the Asia-Pacific and are the region's biggest and third-biggest private banks respectively, according to Asian Private Banker.