Industrial production and retail sales, key indicators of economic activity, cooled sharply last month, according to government data released Wednesday.
That could spook investors, who had been tracking signs of China's recovery earlier this year.
The softness comes as the trade war between the United States and China is back in full swing.
Higher US tariffs on Chinese exports worth $200 billion, enacted last week, have been weighing on markets and are expected to hit growth.
The threat of US tariffs on another batch of exports worth $300 billion looms large.