Mumbai: The Bombay Stock Exchange benchmark Sensex opened 145 points lower on Thursday after investors' confidence was shaken by Wednesday's serial bomb blasts in the country's financial capital, amid a weakening overseas trend.

The 30-share barometer, which had gained 184.40 points in the previous session, fell by 144.82 points, or 0.78 percent, to 18,451.20 in the first five minutes of trade on Thursday.

Similarly, the wide-based National Stock Exchange Nifty index declined by 37.05 points, or 0.66 percent, to 5,548.40, led by information technology and auto stocks.

Investors said a weakening trend on other Asian bourses after Moody's warned that the United States may lose its top-notch credit rating in the coming weeks also dampened the sentiment.

In the Asian region, Hong Kong's Hang Seng index was trading 0.23 percent lower and Japan's Nikkei shed 0.34 percent on Thursday morning.