BEIJING — Chinese stocks fell again today following their sharpest one-day drop in three months, extending declines triggered by government efforts to cool the booming market and avert a price bubble.

The benchmark Shanghai Composite Index opened down 2.9 percent at 3,564.43 following an 8.3 percent fall the previous day. The Shenzhen Composite Index for China's smaller second market opened down 3.7 percent at 1,001.23.

Prices have been falling since Beijing tripled a tax on stock trades last week to cool frenzied trading that had driven up prices more than 50 percent since the start of the year, following a 130 percent climb in 2006.

The boom has prompted millions of first-time investors to jump into the market, tapping savings and retirement accounts and mortgaging homes to buy stocks. Authorities are worried that the new money is fueling a bubble in prices. They say novice investors could be hurt if prices fall sharply.

At today's opening prices, the Shanghai was down 17 percent from its record high of 4,334.92 reached May 29, but it was still up 33 percent from the start of the year.

Yesterday's decline was the sharpest since an 8.8 percent drop Feb. 27 triggered a global selloff.