Equity benchmark Sensex tanked 678 points on Friday, tracking losses in index majors Reliance Industries, Infosys and HDFC Bank amid a weak trend in global markets. The 30-share index plunged 677.77 points or 1.13 per cent to end at 59,306.93. Similarly, the NSE Nifty fell 185.60 points or 1.04 per cent to 17,671.65.