The domestic stock markets opened Thursday's session on a lower note ahead of derivatives expiry amid a global sell-off. The Bombay Stock Exchange (BSE) benchmark index Sensex plunged over 450 points to dip below the 34,000-mark.The wider Nifty50 index of the National Stock Exchange (NSE) cracked below the 10,150-mark. All the sectoral indices, led by realty, metal, capital goods and bank, were trading in the negative terrain. At the time of writing this report, the Sensex had touched day's low at 33,553.18.