China's benchmark Shanghai stock index slumped 4.09 percent at the open on Tuesday, despite a renewed government vow to support the market following the biggest single-day fall in eight years a day earlier.

The Shanghai Composite Index -- which plunged 8.48 percent on Monday -- dropped 152.42 points to 3,573.14. The Shenzhen Composite Index, which tracks stocks on China's second exchange, fell 4.67 percent, or 100.85 points, to 2,059.24.