The Nikkei stock index extended its gains above 2 percent early afternoon Tuesday, as a weakening yen versus the U.S. dollar eased concerns over the outlook for the Japanese currency and boosted exporter issues. At 12:45 p.m., the 225-issue Nikkei Stock Average traded up 830.93 points, or 2.22 percent, from Monday at 38,219.55. The broader Topix index traded 36.46 points, or 1.38 percent, higher at 2,677.60.