The BSE benchmark Sensex was trading 53 points or 0.31 per cent up at 17,131 points when reports last came in.Sensex today shot up by 176 points in early trade, extending gains for the fourth straight session on continued buying by funds and retailers amid a firming trend in Asian markets. In a similar fashion, the wide-based National Stock Exchange Nifty index was trading 13 points or 0.25 per cent up at 5,171 points.