The final reading for the HSBC Purchasing Managers' Survey rose to 51.5 in December, well above the final reading of 50.5 in November and the preliminary reading of 50.9 published in the middle of the month.
November marked the first time in more than a year that the survey crossed above 50 points, the line that demarcates accelerating from slowing growth.
The survey results fit with a growing consensus that the Chinese economy revved back up in the fourth quarter, after growth slowed for the seventh consecutive quarter to 7.4 percent in the third.
A sub-index tracking new orders showed even more room for optimism, rising to 52.9, its highest level since January 2011.
"Such a momentum is likely to be sustained in the coming months when infrastructure construction runs into full speed and property market conditions stabilise," Hongbin Qu, HSBC's chief economist for China, wrote in a note accompanying the survey.
"This, plus Beijing's reiteration of keeping pro-growth policy in place into the coming year, should support a modest growth recovery of around 8.6 percent year-on-year in 2013, despite the ongoing external headwinds."
In another sign of strength, a sub-index tracking output rose to its highest level since May 2011.
The improving economic picture seems primarily linked to domestic demand, as China's export sector continues to grapple with a slowdown in its biggest markets. A new export orders sub-index retreated below 50 in December, after rising into expansionary territory in November for the first time in seven months.
China is on course to achieve growth of 7.7 percent in 2012, according to forecasts in a benchmark Reuters poll, the slowest full year of expansion since 1999.
While that is way above the world's other major economies, it is far below the roughly 10 percent annual growth seen for most of the last 30 years.
The government so far has relied on fine-tuning policy settings in its efforts to combat the worst downturn China had faced since the 2008-09 global financial crisis, studiously avoiding any hint of repeating the 4 trillion yuan stimulus package it launched back then.
Measures to boost growth included injecting liquidity into the financial system through money market operations and accelerating approval of infrastructure projects.
However, while the central government has pledged to continue its strict property market controls, land prices have ticked up in many regions and developers are once again openly marketing luxury second homes, even in the capital. China's property sector directly supports over 40 industries.
Chinese Vice Finance Minister Li Yong, in comments published on December 26, warned of rising risks in the banking sector and pressure on government revenues in 2013.
Regulators are increasingly concerned over the risks posed by investment products that offer higher returns to depositors and investors, and help channel money into China's higher-interest rate shadow banking system.
Economist Michael Pettis of Peking University's Guanghua School of Management warned that even if regulators act to limit the proliferation of wealth management products, China will still see shrinking returns unless it moves away from its investment-led growth model.
"The problem is the inexorable tendency of the current development model to generate debt faster than it generates debt-servicing capacity," Pettis wrote in a recent newsletter.
"Growth in China is currently dependent on an unsustainable increase in debt."
The final HSBC reading precedes a similar survey by the National Bureau of Statistics, which is due to be released on Tuesday, Jan 1.
Copyright @ Thomson Reuters 2012