The 30-share barometer after losing over 423 points in early trade, fell further by 501.34 points, or 2.60 per cent, to slip below 19,000-point level to trade at 18,744.36 points at 1400 hrs.
All the sectoral indices led by realty, metal and banking were trading in the negative zone with fall up to 4.77 per cent.
Similarly, the wide-based National Stock Exchange index Nifty dipped below 5,700 points by losing 153.75, or 2.64 per cent, to trade at 5,668.50.
Besides, a weak opening in the European markets too accelerated selling activity, dragging down the Sensex, they said.