The Sensex fell on Friday to mark its lowest weekly close since January 13 after a sudden slump in Tata Motors and UltraTech Cement shares about 20 minutes before the close spooked investors.
The BSE Sensex fell 0.57 per cent, or 113.79 points, to end at 19,781.19. It lost 1.6 per cent for the week.
The broader Nifty fell 0.59 per cent, or 35.85 points, to end at 5,998.90, closing below the psychologically important 6,000 level, also ending 1.2 per cent lower for the week.
The sudden fall in the share prices of these index stocks added to investor worries after Indian manufacturing slowed to a three-month low in January, and Bharti Airtel Ltd missed its earnings estimates by a wide margin.
Shares also fell on profit-taking after the BSE Sensex added 2.4 per cent in January to post its third-straight monthly gain.
Tata Motors shares fell 5.49 per cent after six separate block deals comprising 2.07 million shares took place at an average price of Rs 274.92. The sales sent the auto maker's shares as low as Rs 268.25.
UltraTech shares fell 3.4 per cent after one block deal of 41,863 shares at an average price of Rs 1,853.80 rupees. They dropped as low as Rs 1,712.35.
Shares in Bharti Airtel, India's top telecoms carrier, fell three per cent, after October-December profit missed estimates by a wide margin.
Bharat Heavy Electricals Ltd shares fell 1.2 per cent after India's top power equipment maker missed analyst estimates with a 17.5 per cent fall in third-quarter net profit, hit by a slowdown in new orders.
Hindustan Unilever fell 1.9 per cent after Morgan Stanley reduced its weightage on consumer staples stocks in its Indian model portfolio by one per cent. It also raised weightage of energy stocks to three per cent.
Satyam Computer Services shares fell 1.6 per cent after Kotak Institutional Equities downgraded it to 'reduce' from 'add', noting October-December revenue growth was 'muted', given the impact from furloughs in the high-tech and manufacturing segments.
Among the gainers, Maruti Suzuki India shares rose 1.8 per cent after reporting better-than-expected January vehicle sales at 114,205 units.
Bajaj Auto shares also rose 1.4 per cent ahead of its monthly sales data.