After a weak opening, the Sensex at the Bombay Stock Exchange lost considerably more ground, and had declined 257 points, or 0.9 percent, to 27,725 in afternoon trade. Similarly, the Nifty at the National Stock Exchange had dropped 57 points, to 8,566. Other key Asian markets in Japan, Hong Kong, South Korea and Singapore had slumped between 1 percent and 1.9 percent. And at the Forex market, the rupee had weakened 20 paise, to 66.93 against the dollar in afternoon trade.