Among bluechip Tata Group stocks, Tata Motors plunged 12.9 per cent, Tata Steel tanked 10.89 per cent and TCS dipped 4.81 per cent on BSE.
Shares of Tata Elxsi plunged 9.21 per cent, Tata Global Beverages (7.26 per cent), Tata Chemicals (5.72 per cent) and Tata Communications (5.34 per cent).
There are fears that the UK operations of several Indian companies might take a hit due to immigration and other restrictions that might come in following Brexit.
In the pre-open trade, the Sensex fell by over 634 points while it opened sharply lower at 26,367.48, 940 points down, and plunged even further to touch a low of 25,944.53 points with a massive decline of nearly 1,058 points or about 4 per cent.
Brexit apart, Tata Sons has been ordered to pay Japan's largest mobile phone firm NTT DoCoMo USD 1.17 billion in compensation for breaching an agreement on its India joint venture.