The BSE Sensex today was down by nearly 181 points to plunge below the 19,000 mark and was trading at 18,860 in afternoon trade. Similarly, the wide-based National Stock Exchange index Nifty also was down by nearly 50 points at 5711 .The Japan's Nikkei fell by 4.67 per cent, while Hong Kong's Hang Seng shed 2.61 per cent. The US Dow Jones Industrial Average ended 0.84 per cent lower in yesterday's trade.