The Nikkei stock index plunged over 2 percent early Wednesday, as investors locked in profits after the benchmark rebounded in its largest point gain the previous day. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average fell 871.22 points, or 2.51 percent, from Tuesday to 33,804.24. The broader Topix index was down 27.82 points, or 1.14 percent, at 2,406.39. On the top-tier Prime Market, decliners were led by mining, transportation equipment and nonferrous metal shares.