MANILA, Philippines -- Some 3 billion Asians could rise to affluent status by 2050 if Asia sustains its present growth momentum and avoids being trapped at middle income levels, according to an Asian Development Bank report.

The report released Wednesday said as the global economy's center of gravity shifts toward Asia, the region could account for about half of world economic output in 2050, up from the current 27 percent, as well as half of trade and investment.

Under an optimistic "Asian Century" scenario, the region's gross domestic product would soar to $148 trillion by mid-century. GDP per person on a purchasing power parity basis would climb to $38,600 compared with the projected 2050 global average of $36,600.

The draft "Asia 2050" report said the less optimistic "Middle Income Trap" scenario assumes that Asia's fast-growing economies of China, India, Indonesia and Vietnam will have slower growth rates and stagnant income levels over the next five to 10 years. It also assumes that none of Asia's slow-growing economies would have faster growth rates.

If these events occur, the report said, Asia would account for only 32 percent or $61 trillion of global GDP in 2050. GDP per capita would also rise to only $20,300, or just over half of what it would be under the more optimistic scenario.

"The difference in outcomes under the two scenarios and thus the opportunity cost of not realizing the Asian Century scenario is huge, especially in human terms," said Haruhiko Kuroda, the Manila-based lender's president.

Under the Asian Century scenario, almost 3 billion Asians would enjoy the fruits of prosperity at least one generation earlier than under the Middle Income Trap scenario, the draft report said.

Some 525 million of nearly 4 billion Asians are currently classified as middle class or come from households that spend between $10 and $100 a day in purchasing power parity terms, comprising 28 percent of the world's middle class population.

China, India, Indonesia, Japan, South Korea, Thailand and Malaysia will lead Asia's march to prosperity, it said. The seven countries' 2010 combined population was 3.1 billion and GDP was $14.2 trillion.

The report warned that poverty still remains pervasive in Asia, with half of all Asians living without basic sanitation and 900 million people in the region with no access to electricity.

The draft report was prepared for ADB's 2011 annual meeting this week in Vietnam.