The Caixin/Markit survey, released on Monday, rose to 50.8 in March from 49.9 in February. A reading above 50 indicates expansion.
Official manufacturing figures published a day earlier also pointed to a jump in activity.
Beijing has taken steps to support the economy to combat slowing growth.
The Caixin/Markit Manufacturing Purchasing Managers’ Index (PMI) rose to an eight-month high of 50.8 in March, beating the 49.9 forecast in a Reuters poll of economists.
The result echoed China’s official PMI data released on Sunday. It showed manufacturing activity rose to 50.5 in March, from 49.2 in February.
The official PMI data looks at activity at larger manufacturers, while the private survey from Caixin and Markit focuses on smaller to medium-sized companies in the sector.
The stronger-than-expected data sent Asian stocks higher. Hong Kong’s Hang Seng index rose 1.7% while the Shanghai Composite jumped 2.3%.
Chinese stimulus
The upbeat factory data indicated that efforts to boost the world’s second largest economy are starting to bear fruit.
China reported its weakest economic expansion in 28 years in 2018, and growth is expected to slow further.
Beijing has unveiled a series of measures – including cutting taxes – to help support the economy.
