The bears have further tightened their grip on the Indian stock market as the benchmark indices extended the losing streak for the third consecutive session on December 18 as investors remained cautious ahead of Fed rate decision outcome tonight.

At close, the Sensex was down 502.25 points or 0.62 percent at 80,182.20, and the Nifty was down 137.15 points or 0.56 percent at 24,198.85.

On the sectoral front, except pharma (up 1 percent), all other indices ended in the red with auto, energy, PSU Bank, metal, media, realty down 0.5-2 percent.

Trent, Dr Reddy's Labs, Cipla, Wipro and Bajaj Auto were top gainers on the Nifty, while losers included Tata Motors, Bharat Electronics, Power Grid Corp, JSW Steel and NTPC.

BSE Midcap and Smallcap indices shed 0.5 percent each.

More than 240 stocks touched their 52-week high on the BSE, including, Bharti Hexacom, EID Parry, KPR Mills, Radico Khaitan, Lloyds Metals, Coromandel International, Coforge, Indian Hotels, BLS Internation, Persistent Systems, 360 ONE WAM, Kaynes Technologies, among others.