The Sensex at the Bombay Stock Exchange fell 52 points, or 0.3 per cent, to 17,413 in opening trade, on Thursday morning, amid weak regional markets, on fears that the euro zone debt crisis may worsen. Later, selling pressure increased, and the Sensex stood 133 points, or 0.8 percent in negative territory, at 17,332 in afternoon deals, a short while ago. The 30-share Sensex has already lost nearly 340 points in the past three trading sessions. Key stock indices in Hong Kong, Indonesia, South Korea, Taiwan and Singapore were down by between 1.4 percent and 1.8 percent, today. Stocks fell as worries about Europe's debt crisis led investors to shed risky assets. But across on Wall Street, the Dow Jones Industrial Average had gained 1.5 per cent, overnight.