Mumbai: The stock market continued to bleed for the sixth straight day on Tuesday under pressure from debt worries in the West, with the benchmark Sensex dropping 558 points in opening trade.

Another benchmark index, the Nifty, slipped below the 5,000-mark for the first time since June 10, 2010, in opening trade. It was trading 172.05 points down within minutes of the opening bell at 4946.45, its lowest level since May 27 last year.

After falling 1,322 points in the past five trading sessions, the Sensex opened on a very weak note on Monday morning, with heavy selling in stocks like Reliance Industries, Infosys, ICICI Bank and TCS.

The Sensex fell to as low as 16,432.00 points, its lowest level since June 1 last year, with a fall of 558.18 points from Monday's close.

The index closed below the 17,000-level on Monday for the first time since June 10, 2010.

The overnight meltdown in the US markets and the continuing downtrend in Asia on Tuesday morning added to the woes of the Indian bourses.

Global markets have been in turmoil for the past two days after the creditworthiness of the US was downgraded by Standard and Poor's amid the American economy's mounting debt worries.

The debt problems in Europe have already been hammering stocks across the world for about a week now.