The CSI300 index of the largest listed companies in Shanghai and Shenzhen fell 1.9 percent, to 3,155.88, while the Shanghai Composite Index lost 2.4 percent, to 2,949.60 points.
Trading was calm in the morning, amid signs that the yuan was stabilising after intervention by China's central bank.
Analysts pointed out, however, that trading volume was thin, signalling that many investors were standing on the sidelines and putting money elsewhere.
Latest data show China's recent stock market rout has further dampened risk taking. Investors have been slashing leveraged bets on stocks, seeking safe haven in bonds and money market funds, and stepping up investment overseas.