The Bombay Stock Exchange benchmark Sensex tanked almost 362 points in opening trade on Monday. The 30-share index, which had lost 271 points in the previous session, plunged further by 361 points, or 2.12 per cent to 16,637 points. The wide-based National Stock Exchange index Nifty dipped below 5,000 points to trade 101.80 points, or almost 2 per cent down at 4,991 points.