China's economic expansion may be far less than official estimates of 6.8 percent and could be closer to 2.4 percent, according to a new report. The gross domestic product (GDP) growth of the world's second-largest economy has slowed steadily since 2010, although levels remain far higher than those achieved by most developed and many developing economies.

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Last month, China's central bank forecast that GDP would slow to 6.8 percent in 2016 from an estimated in 6.9 percent in 2015. However, Fathom, a macro research consultancy based in London, claimed in a report that China's economy is only expanding at 2.4 percent per annum. "We have long questioned the legitimacy of China's official GDP statistics. Pointing to only a mild growth deceleration, we find these impossible to reconcile with a whole host of alternative evidence, not least our own measure of China's economic activity which suggests that growth could be as low as 2.4 percent," Fathom said in the report published Friday entitled "The fantasy and the reality of China's economic rebalancing." This year, global markets remain alert to any hints that China's economic slowdown might be accelerating. Major U.S. stock indexes lost around six percent or more last week, as these fears helped fuel a rout in global stocks.

International analysts and economists have long suspected that Chinese official GDP figures were inflated. Not many have suggested that annual growth could actually be as low as 2.4 percent, however.

The International Monetary Fund, for instance, estimates that China's economy grew by 6.8 percent in 2015 and forecasts it will expand by 6.3 percent in 2016.

"While there is evidence that the old growth engine, powered by manufacturing, investment and exports, has started to stutter, we find far fewer indicators that point to a pickup in consumption. This is contrary to China's official GDP breakdown, which suggests that activity in the tertiary sector is not only the largest as a share of nominal GDP but also the fastest growing, with annual growth outpacing that of both primary and secondary industries," Fathom said. The official GDP data reported by Chinese regional government is particularly questionable. In December, China official news agency, Xinhua, reported that economic levels in parts of China's northeastern rust belt were overstated. One county in Liaoning province posted extra fiscal revenue of 847 million yuan ($129 million) in 2013, 127 percent higher than the real figure, according to media reports.