The Sensex fell below the 10,000 level on the back of heavy selling action, weak global markets and fears of a deep and prolonged recession.
Realty, oil & gas, consumer goods and metal stocks were hammered badly.
The various relief and rescue packages declared by worldwide central banking institutions failed to lift investor response.
At 1:37 p.m., the 30-share index, BSE Sensex stood at 9936.97, down 599.19 points, from its previous closing mark, while the broad-based Nifty slipped to 2971.30, down 176.95 points.