The world added 2.6 million millionaire households last year, showing that the rich are getting richer—and far more numerous, according to a report released Monday. The total number of millionaire households in the world rose 19 percent last year, to 16.3 million, according to Boston Consulting Group's Global Wealth report. Millionaire households represent 1.1 percent of all households globally. The U.S. added the most millionaire households and has the highest total, with a gain of 1.1 million households last year. That brings the total to 7.135 million. China's millionaire population grew to 2.4 million last year from 1.5 million in 2012. But Japan's millionaire population fell by 300,000 to 1.2 million last year, driven mainly by the falling value of the yen versus the dollar. "The key challenge in developed economies is how to make the most of a large existing asset base amid volatile growth patterns," said Brent Beardsley, a BCG senior partner and a co-author of the report. "The task in the developing economies is to attract a sizable share of the new wealth being created there. Overall, the battle for assets and market share will become increasingly intense in the run-up to 2020." Qatar had the highest density of millionaires—175 out of every 1,000 households. Switzerland ranked second in millionaire density (127 per 1,000 households), followed by Singapore (with 100 for every 1,000 households). The U.S. also had the most centimillionaires (those worth $100 million or more), with 4,754 households. But Hong Kong had the highest density of centimillionaires, with 16.8 per 1,000 households. Global financial wealth in the world rose 14.6 percent last year, to $152 trillion—nearly double the rate of growth in 2012. It's expected to grow at least 5 percent a year over the next five years to $198 trillion, with new wealth creation (rather than returns on existing wealth) driving two-thirds of the growth. BCG defines millionaire household wealth as investible assets—cash, deposits and securities. It doesn't include less liquid assets like real estate, business ownership, collectibles and luxury goods. In the Asia-Pacific region, excluding Japan, wealth grew 31 percent, adding more than $8 trillion in 2013. North American wealth grew 16 percent, adding $7 trillion, and Western European wealth rose 5.2 percent, adding $5 trillion. Stocks were the biggest driver of global wealth last year, the report said, with the total wealth held in equities surging by 28 percent.