The BSE benchmark Sensex plunged nearly 290 points in early trade today, extending losing streak for the fourth straight session, on sustained selling by funds amid a weak trend on other Asian bourses.The 30-share barometer, which had lost over 488 points in the last three sessions, plunged further by 289.85 points down at 16,541.23 points with banking, realty, capital goods, metals and auto stocks leading the fall. The wide-based National Stock Exchange index Nifty dipped below psychological 5,000 points level to trade 91.15 points down to 4,995.70 points.In Asia, the Hong Kong's Hang Seng index fell by 2.40 per cent, while Japan's Nikkei was down by 2.60 per in the early trade.