The final HSBC Purchasing Managers' Index (PMI) edged up to 50.2 from August's 50.1, figures on Monday showed.
Although a five-month high and showing the sector was growing, the survey was disappointing for investors as it was well below last week's flash reading of 51.2, with domestic orders weaker than preliminary estimates suggested.
New export orders picked up the slack, climbing to 50.7 from 47.2 in August to be above the 50-point mark separating expansion from contraction. After seasonal adjustments, however, the expansion was slight, HSBC said.
The Australian dollar, a proxy for growth in the world's second-largest economy, fell a quarter of a cent on the disappointment that activity was not as strong as hoped.
"The final reading was weaker than the flash and it showed that activity has weakened in the last 10 days," said Tao Wang, an economist at UBS in Hong Kong, adding a rebuilding of stocks by firms that had led the economic pick-up was slowing.
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On Tuesday, the government releases its official PMI, which is weighted more towards bigger and state-owned companies and generally paints a rosier picture than the private survey, which focuses more on smaller and private sector firms.
The softer-than-expected final HSBC PMI reading was in line with investor bets that China's economy is stabilising, even if the revival is feeble and perhaps short-lived. Indeed, parts of the PMI poll suggested the economy is not out of the woods.
Factories cut jobs for the sixth consecutive month in September. And although output and new orders grew in September, HSBC noted the expansion was fractional after seasonal adjustments. In fact, it said some firms reported a contraction in output, citing unstable economic conditions.
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GRAPHIC: HSBC PMI http://link.reuters.com/tus33v
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STILL STABILISING
Qu Hongbin, a HSBC economist, said action taken by Beijing to shore up growth was helping to lift the economy.
"Growth is bottoming out on Beijing's mini-stimulus," Qu said, noting however that growth in domestic demand was unchanged from August.
Beijing's support and firmer growth in the United States, China's second-biggest export market, have put a floor beneath China's economy, which has slowed in 12 of the last 14 quarters.
To reinvigorate growth, the government has fast-forwarded infrastructure investment, lowered taxes for small companies, and sustained spending in public housing.
But analysts warn the mild pick-up could fizzle if Beijing enacts planned reforms that include curbing state investment.
On Sunday, China opened a free trade zone in Shanghai in what has been hailed as potentially the boldest reform in decades.