The Nikkei index extended its losses in midmorning trading Wednesday, briefly diving over 4 percent, as the overnight release of weaker-than-expected U.S. manufacturing data revived concerns about the U.S. economy. At 10:30 a.m., the 225-issue Nikkei Stock Average fell 1,310.42 points, or 3.39 percent, from Tuesday to 37,375.89. The broader Topix index was down 77.16 points, or 2.82 percent, at 2,656.11. Heavyweight high-tech shares such as Tokyo Electron and Advantest tracked overnight declines by their U.S. counterparts, briefly dragging the Nikkei index down over 1,500 points.