By 1130, Sensex plunged by 40 points at 20,107, and the Nifty down 17 points at 6,088 levels.
On the global front, Japan's Nikkei share average fell further on Thursday afternoon, hitting a five-week low and extending the benchmark's losses to more than 14% since last Thursday's plunge.
The Nikkei skidded as much as 5.1% to 13,600.92. The index was down 4.8% at 13,636.74 by 0530 GMT.
The benchmark dived 7.3% on May 23, the biggest single-day loss since the March 2011 earthquake and tsunami. Still, it is up 31% so far this year, underpinned by aggressive government and central bank policies to revive the economy.
Back home, the rupee today strengthened by 10 paise against the US dollar to 56.07 in early trade at the Interbank Foreign Exchange market on the back of euro's gains against the American currency overseas.
According to Ravi Nathani, technical analyst, Nsetoday.com, “Near term pattern indicates a top has been made on charts (6128), trade above this level would add trigger in the direction. Expect some profit booking in the day”.
On the sectoral front, BSE Realty index has declined by almost 3% followed by counters like Consumer Durable, Oil & Gas, TECk, Metal, IT and Banks, all declining between 1-2%. However, BSE Auto index has surged by almost 1%.
The main losers on the Sensex at this hour include Cipla, ICICI Bank, Tata Steel, Bharti Airtel, Hero Moto, Maruti Suzuki, ONGC, Infosys and RIL, all declining between 1-4%.
Shares of Cipla were down 2% at Rs 393 after the company late Wednesday reported 8.3% decline in its net profit at Rs 267.56 crore for the fourth quarter ended March 31, 2013 because of higher tax expenses.
On the gaining side, Tata Motors, M&M, ITC, HDFC and Sun Pharma had gained between 1-3%.
Tata Motors raced up nearly 3% as the company pruned losses at the stand-alone level, thanks to the strong performance by Jaguar Land Rover (JLR).
Among other shares, BEML was up nearly 8% at Rs 181 after the company reported robust earnings in the fourth quarter ended March 31, 2013 against a huge loss in the same quarter last year.
The market breadth in BSE remains weak with 1,030 shares declining and 693 shares declining.