The number of millionaires will soar by more than 70 per cent over the next decade, and they will control more than US$200 trillion ($252.5 trillion) in assets, twice as much as they do now, according to consulting firm Deloitte.

The study, aimed at encouraging investment by banks in wealth management services for the super-rich, also concluded that China will enter the top 10 of countries with the most millionaires. Mexico, home to the world's richest man, Carlos Slim, is forecast to move into the top 20.

However, the dominance of the United States and the rest of the developed world will continue, Deloitte said.

It predicts there will be 20.6 million millionaire households in the United States in 2020, up from 10.5 million now, controlling US$87.1 trillion of assets. The number of British millionaires is set to grow from 2.9 million to 3.8 million - keeping the country in fourth position.

"Which countries may offer the most promising future and how wealth managers can potentially increase profitability in the next decade are important questions for a wide range of financial institutions," said Andrew Freeman, executive director of the Deloitte Centre for Financial Services.

"Identifying and understanding how different market segments are changing can help formulate growth strategies."

Hong Kong is likely to have the highest density of millionaires in 2020, with 47 per cent of the population holding more than US$1 million, followed by Singapore with 37 per cent and Switzerland on 24 per cent.

The study defined wealth as financial assets, such as stocks and bonds, and non-financial assets including primary residence.

- Independent