Mumbai: Indian stocks plunged deep into the red on Monday morning as the Sensex lost more than 500 points within minutes of the market opening on concerns over the US losing its top-notch credit rating due to mounting debts.

The 30-share benchmark index dropped within minutes of opening to 16,793.07 points, its lowest level since June, 2010, registering a fall of 512 points from its previous close.

The NSE's Nifty was also down by 131 points at 5,079.65 points at 0930 hours, after hitting a low of 5,060.05 points earlier on Monday morning.

Stocks like Tata Motors, TCS and Wipro dropped more than 5 percent, while RIL, ICICI Bank, Tata Steel and Bharti airtel were also trading sharply lower.

The sharp fall came in the first trading session after the US lost its 'AAA' credit rating for the first time in history, as ratings agency S&P was not convinced with the efforts being made to tackle the country's debt problems.

Monday's fall follows an over 1,000-point decline in the Sensex over the last four trading sessions amid weak global cues.