Yes Bank was top loser in the Nifty 50 basket of share, the stock dropped 7.14 per cent to Rs 55.25.

The S&P BSE Sensex and NSE Nifty 50 indexes extended losses ahead of derivatives expiry for the month of August paced by declines in banking and financial services shares. The benchmarks opened lower and the selloff deepened in noon deals wherein the Sensex plunged over 400 points and the NSE Nifty 50 index dropped below important psychological level of 10,950. HDFC, ICICI Bank, Reliance Industries and State Bank of India were among the top drags on the Sensex.

As of 12:42 pm, the Sensex traded 348 points or 0.9 per cent lower at 37,104 and the NSE Nifty 50 index tumbled 97 points or 0.88 per cent to 10,948.

Sixteen of 19 sector gauges compiled by BSE were trading lower led by the S&P BSE Bankex index's 1.6 per cent fall.

S&P BSE Power, Finance, metal, basic materials and energy sector gauges also fell between 0.8-1.5 per cent each.

On the other hand, S&P BSE Information Technology index was top gainer, up 0.12 per cent.

Mid- and small-cap shares were also witnessing selling pressure as the S&P BSE MidCap and S&P BSE SmallCap indexes fell nearly 1 per cent each.

Yes Bank was top loser in the Nifty 50 basket of share, the stock dropped 7.14 per cent to Rs 55.25 after the credit ratings agency Moody's downgraded its long-term foreign-currency issuer rating to "Ba3" from "Ba1". Moody's has also downgraded the bank's long-term foreign and local currency bank deposit ratings to "Ba3" from "Ba1", foreign currency senior unsecured MTN program rating to "(P) Ba3" from "(P) Ba1", and adjusted baseline credit assessment (BCA) to "b1" from "ba2".

Indiabulls Housing Finance, ICICI Bank, State Bank of India, Grasim Industries, Tata Steel, Mahindra & Mahindra HDFC, Hindalco, Tata Motors and Cipla were also among the losers, down 1.55-6 per cent each.

On the flipside, Sun Pharma, Bharti Infratel, Eicher Motors, Vedanta, infosys and Coal India were among the notable gainers.

The overall market breadth was extremely bearish as 1,167 shares were falling while a little over 500 were advancing on the NSE.