Extending losses for the third straight day, the Sensex at the Bombay Stock Exchange declined 120 points in early trade on Thursday to 21,051, on sustained selling by funds amid weak trend in other Asian markets.The 30-share barometer had lost 155 points in previous two sessions.The Nifty at the National Stock Exchange declined 37 points to 6,272.Among other Asian markets, Hong Kong's Hang Seng index was down 0.55 per cent and Japan's Nikkei shed 1.61 per cent in morning trade.The US Dow Jones Industrial Average ended 0.81 per cent lower in Wednesday's trade.