The BSE benchmark index Sensex surged by 138 points in early trade today on sustained buying by funds and retail investors triggered by a firming trend on other Asian bourses. The 30-share index gained 138 points to trade at 20,424, with all the sectoral indices rising up to 1.14 per cent.The wide-based National Stock Exchange index Nifty rose by 30.65 points to trade above 6,200-level at 6,218.In Asia, Hong Kong's Hang Seng index rose by 1.30 per cent, while Japan's Nikkei was up by 1.38 per cent in early trade. The US Dow Jones Industrial Average ended 0.80 per cent higher in Friday's trade.