The Shanghai Composite closed down 8.5% at 3,725.56 after more weak economic data raised concerns about the health of world’s second largest economy.
Profit at China’s industrial companies dropped 0.3% in June from a year ago.
That followed data on July 24 indicating that factory activity in July seen its worse performance for 15 months.
The Shanghai market’s fall was the biggest one-day loss since February 2007.
While there was little to explain why shares were being sold at such a level, analysts said fears that China might hold off from further measures to boost the economy had contributed to concerns among investors.
The stock market has been benefitting from a series of support measures from the government and regulators after it lost a third of its value in the three weeks from mid-June.
Since late June, Chinese authorities have cut interest rates, suspended initial public offerings, eased margin-lending and pushed brokerages to buy stocks, backed by money from the central bank.
Chinese shares had recovered about 15% of their value before today’s plunge – showing some signs of stabilization.
On July 27 stocks fell across the board, including benchmark index heavyweights such as China Unicom, Bank of Communications and PetroChina.
More than 1,500 shares listed in Shanghai and Shenzhen fell by their daily downward limit of 10%.
Elsewhere in Asia, Hong Kong’s Hang Seng index closed down 3.1% at 24,351.96 – its biggest loss in three weeks.
Japan’s benchmark Nikkei 225 index fell 1% to 20,350.10, while South Korea’s Kospi index finished 0.4% lower at 2,038.81.
Australian stocks bucked the downward trend, closing up 0.3% at 5,582.40.
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