The number of millionaires worldwide will grow more than 70% by 2020 with the U.S. expected to have double the total number of families with a net worth of over $1 million, according to a report by the Deloitte Center for Financial Services.

The study, conducted with Oxford Economics, aimed to identify which countries may offer the most promising future to help financial institutions increase profitability in the next decade by encouraging investment by banks in wealth management services for the super-rich.

"Identifying and understanding how different market segments are changing can help formulate growth strategies." said Andrew Freeman, the executive director of the Deloitte Centre for Financial Services.

The U.S. and Europe have the greatest concentrations of wealth than any other region, although emerging markets are narrowing the gap.

According to the report, China will lead the way in the rapid rise in the number of millionaires, followed by Brazil and Russia.

By 2020, China and South Korea will be among the top 10 of countries with the greatest total number of families worth more than a million dollars. China is expected to rank No. 7, with 2.5 million millionaire households.

"There is going to be very fast growth, but it will take a lot longer to reach anything like the wealth in the developed world," said Freeman, also lead author of the report.

Despite the recession, the US still currently dominates the pack with 10.5 million millionaire households. The number is expected to reach 20.6 million in 2020 with 43%of the world's wealth, maintaining the U.S.'s position in the top spot.

Japan is expected to rank a distant second, with 8.6 million millionaire households in 2020.

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