(Yicai Global) Sept. 17 -- Shares in natural gas and dye companies were the top performers among the Chinese mainland exchanges today as the three major benchmarks fell.

The Shanghai Composite Index slid below the psychologically important milestone of 3,000, closing 1.73 percent lower at 2,978.12 with investors trading CNY237.7 billion (USD33.5 billion) worth of shares. The Shenzhen Component Index slipped 1.97 percent to 9,722.80 with trading volume of CNY348.2 billion, and the ChiNext Price Index, which tracks emerging companies listed in Shenzhen, fell 2.12 percent to 1,677.99 as investors swapped CNY123.2 billion in shares.

The chipmaking and software sectors were the biggest losers.