The Bombay Stock Exchange benchmark Sensex lost nearly 300 points in opening trade today amid panic selling in markets worldwide following the US Federal Reserve's warning that the outlook for the world's largest economy is grim.The 30-share index fell by 299.62 points, or 1.75 per cent, to 16,765.53 in the first few minutes of trade today.The wide-based National Stock Exchange Nifty index also plunged by 93.25 points, or 1.81 per cent, to 5,040 in opening trade. In the Asian region, Japan's Nikkei index was trading 2.12 per cent lower, while Hong Kong's Hang Seng Index tumbled by 4.11 per cent in early trade today. The US Dow Jones Industrial Average closed 2.49 per cent lower in yesterday's trade.