The S-P BSE Sensex and NSE Nifty 50 indexes fell for fifth session in a row on Thursday as traders lightened their positions ahead of Union Budget on Monday.

Volatility was high during the session as futures and option contracts for the month of January expired.

The benchmarks staged a gap down opening and extended losses wherein the Sensex fell as much as 891 points and Nifty 50 index briefly fell below its important psychological level of 13,750.The Sensex ended 536 points or 1.13 per cent lower at 46,874.36 and Nifty 50 index dropped 150 points to settle at 13,818."It is a healthy correction from record highs and looking at the derivative rollovers it seems traders are lightening their positions ahead of the Budget which is a good sign to go into a major economic event," AK Prabhakar, head of research at IDBI Capital told TheIndianSubcontinent.Foreign institutional investors also resorted to selling as they sold shares worth Rs 673 crore on Thursday, data from NSDL showed.HDFC Bank, Infosys, Hindustan Unilever, HDFC and TCS were among the top drags on the Sensex, they collectively wiped out over 400 points from the Sensex.Eight of 11 sector gauges compiled by the National Stock Exchange ended lower led by the Nifty IT index's over 2 per cent fall.

Nifty Auto, FMCG, Pharma, PSU Bank and Realty indexes also fell between 1-2 per cent.Hindustan Unilever was top Nifty loser, the stock fell 3.65 per cent to settle at Rs 2,304 after its profit rose 19 per cent to Rs 1,919 crore in December quarter.Maruti Suzuki declined 3.44 per cent to end at Rs 7,600 as drop in quarterly margins on Thursday as rising costs took the shine off an uptick in demand.Wipro, HDFC Bank, Power Grid, HCL Technologies, Kotak Mahindra Bank, Bajaj Finserv, Divi's Labs, UPL, Infosys and IndusInd Bank also fell between 2-3 per cent.On the flipside, Axis Bank, State Bank of India, Indian Oil, Bharat Petroleum, GAIL India and ICICI Bank were among the notable gainers.