The official manufacturing purchasing managers’ index (PMI) dropped to 49.7 from 50 in July.
A figure below 50 indicates contraction.
The weak data is likely to add to global concerns over China’s economy losing steam and could send Asian and global shares down further.
A separate private Caixin/Markit index also released on Tuesday puts the PMI number even weaker, at 47.3, the weakest reading since 2009.
The fresh economic data is also likely to undermine efforts by Beijing to reassure investors and calm markets.
Chinese mainland stocks have been on a steep downward slope over the past months, shedding almost 40% since June.
Authorities have injected money into the markets, allowed the state pension fund to start buying up shares and lowered lending rates.
So far though, none of those measures have managed to push the markets back into positive territory and analysts have warned that the more Beijing’s intervention fails to have an impact, the more likely it is that future ones will be shrugged off by investors.
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