The BSE benchmark Sensex fell by nearly 159 points in opening trade today, extending yesterday's losses.The 30-share index, which ended 158.79 points lower in the previous session, fell by another 158.77 points, or 0.99 per cent, to 15,849.57 in opening trade.In a similar fashion, the wide-based National Stock Exchange Nifty index declined by 50.30 points, or 1.01 per cent, to 4,754.80.In the Asia region, Hong Kong's Hang Seng Index was trading 0.73 per cent lower, while Japan's Nikkei shed 0.83 per cent in morning trade today.