The Hang Seng Index plunged 3.67 percent, or 1,140.82 points, to 29,930.23, while the benchmark Shanghai Composite Index fell 2.78 percent, or 90.71 points, to 3,172.77 and the Shenzhen Composite Index, which tracks stocks on China's second exchange, dropped 3.09 percent, or 57.22 points, to 1,792.38.