The BSE benchmark Sensex which rallied by almost 197 points in opening trade on Friday stood 335 points up at 18686 points a short while ago, extending gains into the fourth straight session. The sentiments were driven by sustained buying by funds, and the firming trend overseas. Stocks in the IT, realty banking, auto and metal sectors, led the rally. Similarly, the broad-based National Stock Exchange Nifty index stood 91 points up at 5,614 points in afternoon trade. Japan's Nikkei Index was up by 1.38 per cent and Hong Kong's Hang Seng Index was up by 0.81 per cent in early trade on Friday. In the US, the Dow Jones Industrial Index ended 0.70 per cent higher on Thursday.