Equity benchmark Sensex tumbled 257 points on Wednesday tracking losses in index majors HDFC Bank, ICICI Bank and Kotak Bank amid a negative trend in global markets ahead of the US Fed's policy outcome.

The 30-share index ended 257.14 points or 0.43 per cent lower at 59,771.92. Similarly, Nifty fell 59.75 points or 0.33 per cent to 17,829.20.

Sun Pharma was the top loser in the Sensex pack, falling over 3 per cent, followed by IndusInd Bank, Bharti Airtel, Kotak Bank, ICICI Bank and HDFC Bank.

On the other hand, L&T, Asian Paints, UltraTech Cement, SBI and Bajaj Finance were among the gainers.

"After a sideways movement post its positive opening, the indices took a downturn as major global indices traded weak ahead of the US Fed policy announcement, said Vinod Nair, Head of Research at Geojit Financial Services.

The Fed is expected to announce the tapering of its asset purchase program in the near-term while any hint on interest rate reversal is keeping investors on the edge. Any indications showing a faster rate of tapering will have a negative effect on the equity market. Or else, we can expect a reversal from this weak trend, he noted.

Elsewhere in Asia, bourses in Shanghai, Hong Kong and Seoul ended with losses, while Tokyo was closed.

Stock exchanges in Europe were also trading on a negative note in mid-session deals.

Meanwhile, international oil benchmark Brent crude fell 1.66 per cent to USD 83.31 per barrel.