The BSE benchmark Sensex tumbled by over 334 points in opening trade today. The 30-share Sensex, which lost nearly 389 points in Thursday's trade, plunged by 334.27 points, or 2.02 per cent, to 16,153.97 in opening trade today. In a similar fashion, the wide-based National Stock Exchange Nifty index declined by 91.20 points, or 1.84 per cent, to 4,852.45.