Nikkei plunged sharply on Thursday, as investors unloaded shares amid concern about overheating, while Canon tumbled following a weak earnings report. The 225-issue Nikkei Stock Average lost 168.35 points, or 1.14 percent, from Wednesday at 14,562.93. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was down 17.60 points, or 1.44 percent, at 1, 202.32. Almost all 33 sectors declined led by insurance, utilities and consumer finance issues, while Airlines and oil companies were the only gainers. The turnover was about 2,067.3 billion yen (about 20.61 billion dollars).