The Bombay Stock Exchange benchmark Sensex fell over 172 points in opening trade today. The Sensex was trading at 17513, down by over 187 points when reports last came in. Similarly, Nifty of National stocks exchange was down by over 60 points at 5252. Brokers said trading sentiment turned bearish on selling by funds and profit-booking by retail investors amid weakening global markets. The US Dow Jones Industrial average ended almost one per cent down in yesterday's trade, while Hong Kong's Hang Seng Index was 0.59 per cent lower. Japanese Nikkei index fell by 2.18 per cent in early trading today.