Extending losses for the third straight day, the Sensex at the Bombay Stocks Exchange tanked over 325 points to dip below the 18,000 level in the early trade today, to 17,982 points. The fall is attributed to sustained selling, as rupee plunged to fresh lows amid a weakening trend overseas. All sectoral indices led by financials and realty trading in negative territory with fall up to 3.08 per cent. The 30-share index had lost over 1,060 points in the previous two sessions. The Nifty at the National Stock Exchange slipped below 5,400 points mark by falling 92 points to 5,323. In the Asian region, Hong Kong's Hang Seng index was down 0.30 per cent, while Japan's Nikkei Index shed 0.53 per cent in the morning trade today. The US Dow Jones Industrial Average ended 0.47 per cent lower in yesterday's trade.