Sensex down 510pts; HDFC, RCom shed 6%

 ACC, Mahindra & Mahindra, Satyam and ICICI Bank are down over 3% each to Rs 988, Rs 774, Rs 479 and Rs 916, respectively.

Ranbaxy is the sole gainer among the index stocks and is up 1% at Rs 377.

Out of 2,350 stocks traded so far, 1,869 have declined, 445 have advanced and 36 are unchanged.