China's stock indexes slumped when the market opened Thursday with greatest drop in nearly a year.

The Composite Stock Index on the Shanghai Stock Exchange closed at 1,332.94 points, down 53.78 points or 3.88 percent. The Component Stock Index on the Shenzhen Stock Exchange closed at 3,312.27 points, down 134.49 points.

Stock indexes for small and medium-sized companies listed on the Shenzhen Stock Exchange saw overall decline, triggering the slump of securities board of science and technology.

However, exchange volume on both securities markets expanded Thursday, with trade on the Shanghai Stock Exchange reaching 11.742 billion yuan (1.42 billion US dollars) and that on the Shenzhen Stock Exchange reaching 8.026 billion yuan.

No policy that could have caused the decline had been issued recently, said insiders. Instead, they acknowledged, the market was adjusting itself to shake off the influence of previous rises.

The market remains in fluctuation, and it is possible for those who benefited from the previous market rise to sell their stocks, they said.