A Chinese investor is pictured in front of a screen displaying prices of shares (green for price falling) at a stock brokerage house in Jiujiang city, East China's Jiangxi province, Aug 25, 2015. [Photo/IC]

Stocks plunged further on Tuesday to extend the steepest four-day rout since 1996 on concern that authorities are withholding market support measures.

The benchmark Shanghai Composite Index sank 7.6 percent to close at 2,964.97, falling below the 3,000 level for the first time in eight months. The gauge has lost 22 percent over the past four days.

More than 1,000 stocks slid by the daily limit of 10 percent on Tuesday, including China National Petroleum Corp and Sinopec Group, the country's State-owned oil giants and heavily-weighted blue-chips of the Shanghai gauge.

Banks including CITIC Bank, Bank of Communications, Everbright Bank, Ningbo Bank and Nanjing Bank dived by more than 9.5 percent.

The ChiNext Index, tracking China's NASDAQ-style board of growth enterprises, plummeted 7.5 percent to 1,990.71 on Tuesday.

Turnover continued a downward trend, with 358.7 billion yuan of stocks changing hands at the Shanghai exchange. The extending balance of margin trading dropped for a fifth day by 6 percent as of Monday, latest data by the bourse showed.

The Shanghai gauge plunged after sinking 12 percent last week, despite the State Council granting pension funds access to equities for the first time over the weekend.

The A-share rout sent global stocks staggering, as the S&P 500 and the Dow Jones Industrial Average slid 3.9 and 3.6 percent respectively on Monday amid volatility.