A reading above 50 indicates expansion, while a reading below that represents contraction.
The sub-index on manufacturing output retreated to a 45-month low of 46.6 in August from 47.1 in July, according to the survey of Caixin Media Co., Ltd.
"The Caixin Flash China General Manufacturing PMI for August has fallen further from July's two-year low, indicating that the economy is still in the process of bottoming out," said Dr. He Fan, chief economist at Caixin Insight Group.
The flash index is published on a monthly basis ahead of final PMI data, making it the earliest available indicator of manufacturing conditions in China.
The estimate is based on approximately 85 to 90 percent of total PMI survey responses from over 420 manufacturing companies each month and is designed to provide an indication of the final PMI.