The crack on Dalal Street widened after reports that serial blasts hit the IT city of Bangalore.
There was no immediate word of casualties reported yet.
Banking and oil & gas stocks were battered. Smallcaps and midcap stocks were relatively affected.
At 1:30 am, the Bombay Stock Exchange's Sensex tumbled 552 points or 3.73 per cent to 14,225.24. The index touched a high of 14,484.39 and low of 14,210.63 in trade so far. BSE Midcap and Smallcap indices were down 0.34 per cent and 0.38 per cent respectively.
Biggest index losers were ICICI Bank (-10.42%), HDFC (-7.16%), Reliance Industries (-7.13%), HDFC Bank (7.09%) and Reliance Infrastructure (5.68%). Ranbaxy Laboratories (2.81%), Hindustan Unilever (2.26%), ACC (1.49%), NTPC (1.13%) and Satyam Computer (0.99%) were the major gainers.
The National Stock Exchange's Nifty slumped 118 points or 2.67 per cent to 4315. The index touched a low of 4297.15 after opening at 4440.85.