The Asian Development Bank Wednesday slashed its growth estimates for the region's emerging economies to the lowest level since 2009, citing a slowdown in powerhouses China and India.

The bank also warned of significant risks caused by the effects of the European debt crisis and continued weakness in the United States, both of which are major export markets.

China's gross domestic product (GDP) was tipped to expand 7.7 percent this year before bouncing back to 8.1 percent in 2013, but still well below the 9.3 percent achieved last year, the bank said in an update to its Asian Development Outlook 2012 report.

India would see GDP growth slow to 5.6 percent in 2012 before picking up to 6.7 percent next year.

"Dimming global growth prospects and soft domestic demand in the region's two largest economies are slowing the pace of developing Asia's expansion," the Manila-based lender said.

The bank cut its 2012 growth forecast for developing Asia, which comprises 45 nations, from 6.9 percent in April to 6.1 percent – the lowest since 2009 when the region expanded 6.0 percent.

It also revised downward the 7.3 percent growth outlook for 2013 to 6.7 percent. The region expanded 7.2 percent in 2011.

"Developing Asia is slowing down much more than we expected," ADB chief economist Changyong Rhee told reporters in Hong Kong as the bank released the report.

"The years of two-digit growth in Asia are coming to an end," he said, but added that there was no need for "panic".

"This is a natural adjustment to a more sustainable growth pace," he said.

The eurozone debt crisis and a looming fiscal cliff in the United States – a predicted huge cut in the budget deficit and corresponding slowdown in the economy – could have "disastrous spillovers" to the rest of the world, and remain the biggest risks for emerging Asia, he said.

Rhee added that the region – long seen as an oasis of opportunity on the gloomy global economic landscape – "must brace for a prolonged period of moderate expansion" after years of rapid growth.

He urged countries to diversify their revenue sources, paying particular attention to job-creating services. The service sector accounted for almost half the region's GDP in 2010.

East Asia was still the fastest-growing sub-region, with forecast growth of 6.5 percent this year and 7.1 percent in 2013.

Growth in Southeast Asia would be resilient, mainly due to Thailand's recovery from the severe flooding in 2011 and higher government spending in Malaysia and the Philippines.

"Overall we are very optimistic that Asia will maintain its growth momentum, even though we may not be able to expect two-digit growth rates as we have seen in the past two decades," Rhee said in a statement on the ADB's website.

The ADB said the projected slowdown however was likely to ease price pressures, with inflation expected to fall from 5.9 percent in 2011 to 4.2 percent in 2012 and 2013, if there are no spikes in commodity prices.