The Sensex at the Bombay Stock Exchange declined 173 points, or 0.9 percent, to 18,629 in early trade, today, on sustained selling by investors, amid falling regional markets. Later, the Sensex lost some more ground, and stood 234 points, or 1.2 percent in the red, at 18,568 in afternoon trade, a short while ago.Stock markets in Japan, Singapore, Indonesia, and South Korea had fallen between 0.3 percent and 1.8 percent, today. Wall Street's Dow Jones Industrial Average had ended 0.8 per cent lower in yesterday's trade.