The flash Caixin China Manufacturing Purchasing Managers' Index (PMI) retreated from 49.4 in June to 48.2 in July, the lowest since April in 2014.
A reading above 50 indicates expansion, while a reading below that represents contraction. The sub-index on manufacturing output is 47.3 in July, a 16-month low, and down from 49.7 in June.
The manufacturing output index and the new order index hit record lows in more than one year, indicating the foundation for economic recovery is not stable and the manufacturing sector is still in difficulties, said Qu Hongbin, chief China economist with the Hong kong and Shanghai Banking Corporation (HSBC).
The data may bring pressure for China to continue with its loose monetary policies, Qu said.
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China's economy posted 7 per cent growth year on year in the second quarter, unchanged from the first quarter, but better than market predictions.
HSBC held the sponsorship for five years, and CLSA sponsored the Markit China PMI prior to HSBC.
The flash index is published on a monthly basis ahead of final PMI data, making it the earliest available indicator of manufacturing sector operating conditions in China.
The estimate is based on approximately 85 to 90 per cent of total PMI survey responses each month and is designed to provide an indication of the final PMI.
China's recent stock market crash in June 12, wiped out about three trillion dollars of capital. The fall sent a warning to China's economy that has already faced downward pressure such as sluggish external demand and weak investments.
The slump prompted China's securities watchdog to order probe into the market manipulation activities of Chinese stock and futures trading.
The stock market had lost around 29 per cent of its value since its peak of 5,178.19 points.