New Delhi, Nov 26 : India's key equity indices -- S&P BSE Sensex and NSE Nifty50 -- closed sharply lower on Friday as a new variant of Covid-19 emerged in South Africa, analysts opined. The barometer 30-scrip Sensex closed at 57,107 points, down by 1,687 points or 2.87 per cent. Similarly, the broader 50-scrip Nifty closed the day at 17,026 points, down by 509 points or 2.91 per cent. Notably, the Central government on Thursday told all the states and Union Territories to be cautious about international passengers travelling from or through Botswana, South Africa and Hong Kong in view of a new Covid variant detected in South Africa. Many other countries too have raised concerns about the potential spread of this new variant and are closely monitoring the matter. Shares of JSW Steel, Tata Motors, Hindalco, Adani Ports, Indusind Bank were the top losers during the session, NSE data showed. As per the information available on the NSE website, stocks of these companies closed 7.48 per cent, 6.77 per cent, 6.57 per cent, 6.22 per cent and 6.19 per cent lower, respectively. On the other hand, despite weak broader market sentiment , pharma stocks such as Alkem Laboratories, Cadila Healthcare, Dr. Reddy's, Divi's Laboratories, Cipla among others rose considerably during the session, possibly due to the emerging of the new variant which may boost demand for pharma sector, analysts said. /IANS