The Sensex at the Bombay Stock Exchange plummeted 543 points, or 2.8 percent, to 18,824 in afternoon trade, a short while ago, on across-the-board selling pressure, amid a falling rupee and declining global bourses. Earlier in the morning, the Sensex had opened with a loss of 146 points, or 0.7 percent, to 19,222 as funds and retail investors booked profits after recent gains. The 30-share Sensex had climbed over 700 points in the previous four trading sessions.Key stock indices in Japan, China, Hong Kong, South Korea and Singapore had lost between 0.1 percent and 0.8 percent, today. The US Dow Jones Industrial Average had ended 1.5 per cent lower in yesterday's trade.