Sensex tumbles over 500 points in opening trade; Nifty below 13,800

HDFC Bank was the top loser in the Sensex pack, shedding around 2.50 per cent, followed by HDFC, HCL Tech, Tech Mahindra, Sun Pharma, PowerGrid, Kotak Bank, SBI, and Nestle India. On the other hand, ONGC, NTPC, Reliance Industries and HUL were among the gainers.