The Sensex at the Bombay Stock Exchange declined by 166 points in early trade today, as funds and retail investors preferred to book profits, after six sessions of gains, amid a weak trend in global markets. The 30-share barometer, which had surged by over 470 points in the last six sessions, fell by 0.87 per cent, to 18,736 in opening trade today.The Nifty at the National Stock Exchange fell by 66 points to 5,694.In Asian region, Japan's Nikkei Index was down 1.64 per cent, while Hong Kong's Hang Seng index shed 1.28 per cent in early trade.The US Dow Jones Industrial Average ended 2.36 per cent down in yesterday's trade.