The Bombay Stock Exchange benchmark Sensex extended its gains in opening trade on Monday, rising by over 63 points. This follows fund and retail investor-buying, driven by a firming trend in the Asian region. The 30-share index, which gained nearly 253 points in the previous four sessions, added 0.34 per cent, to 18,194.09 points in morning trade. The wide-based National Stock Exchange index Nifty also surged 17.15 points, to 5,466.25 points. Meanwhile, the Hong Kong Hang Seng Index rose by 0.26 per cent and the Japan Nikkei index was trading higher by 0.90 per cent in early trade on Monday.