The 30-share barometer fell by 301.70 points, or 1.68 per cent, to 18,094.27 points in the first few minutes of trade today. The Sensex had lost 755 points in the previous three sessions.
Similarly, the wide-based National Stock Exchange Nifty index declined by 79.55 points, or 1.44 per cent, to 5,432.60.
Brokers said continued offloading of positions by funds and retail investors, tracking a weakening trend in the rest of Asia in the wake of sharp losses registered in the US market on Friday due to concerns over the protests in Egypt, besides the weak results of blue-chip companies, dampened the trading sentiment in the domestic market.
All the sectoral indices were trading in the negative zone, witnessing losses of up to 2.75 per cent.
In other Asian markets, Japan`s Nikkei was down by 1.63 per cent, while Hong Kong`s Hang Seng index was down by 1.20 per cent. The US Dow Jones Industrial Average ended 1.39 per cent lower on Friday.