Extending its losses for the fifth straight session, the Sensex at the Bombay Stock Exchange closed 79 points, or 0.5 percent lower, at 16,780, today, on sustained weakness in the global markets. The Nifty at the National Stock Exchange fell 28 points, or 0.6 percent, to 5,008. Stock markets in Japan, China, Singapore, Hong Kong, and South Korea fell between 0.3 percent and 1 percent.