General Motors on Thursday forecast a sharp slowdown in car sales growth this year in China and India, the world's two fastest-growing major markets.

The US automaker said it expected auto sales would rise 10-15 percent in both Asian giants, down from 32 percent expansion last year in China and 31 percent in India.

"These growth rates of 30 percent in China are just not sustainable," GM International Operations President Tim Lee told reporters in New Delhi. "We see sales growth slowing to 10-15 percent in China and India," he said.

China, where 18.06 million units were sold in 2010, emerged as the US automaker's biggest market last year, eclipsing the United States.

"Even 10 to 15 percent growth on such a huge base makes China a vast market," Lee said.

China has witnessed a decade of nearly non-stop annual sales growth of 30 percent or more as rising income levels fuelled by a fast-growing economy prompted a surge in car purchases.

The removal of subsidies on small-engine cars this year was expected by experts to cool sales.

India, the world's seventh largest auto market, has also become a battlefield for US, Asian and European automakers.

With only one in 10 households in urban areas owning a car and one in 50 in rural areas, the number of units sold in India was far lower at 1.9 million in 2010.

GM said sales in India, which grew by an average 24 percent annually during the past decade, were likely to fall because of aggressive interest rate increases aimed at clamping down on surging inflation.

"Unless we see a reversal in commodity prices and interest rates, I do see a downtown as far as 2011 is concerned," said GM India head Karl Slym.

Even with the overall Indian market expected to slow, General Motors forecast its own vehicle sales would triple to 300,000 units by 2013, from about 110,000 units now.

GM has a 13-percent market share in China and four percent in India.