The Sensex at the Bombay Stock Exchange declined 168 points, or 0.9 per cent, to 18,451 in opening trade, this morning, on sustained selling by funds and retail investors, amid falling global markets. Later, the Sensex remained weak, and stood 191 points, or 1 percent in negative territory, at 18,428, in afternoon deals, a short while ago. The 30-share Sensex had lost over 280 points in the previous four trading sessions. Key stock indices in China, Hong Kong, Singapore, Taiwan and South Korea had lost between 0.1 percent and 1 percent, today. The US Dow Jones Industrial Average had tumbled 1.5 per cent in yesterday's trade, as investors worried about Washington's fiscal cliff.