The 30-share index Sensex turned volatile during noon amid lingering worries on the European debt crisis and pessimistic reactions at other global stock markets.

The Sensex, which opened at 16,574.79, was trading 68.06 points up at 16,640.09 as against its last close at 16,572.03.

The broad-based Nifty stood at 4,987.25 after surging 0.34% from its previous close at 4,970.2.

Broader markets indices remained weak, with the BSE midcap index trading 0.06% up and the BSE smallcap index 0.28% higher.

Among other Asian stock markets, the Japanese Nikkei marked its closure at 9,603.24, down 1.12%, after PM Yukio Hatoyama said he would step down, two months before elections.

PM's declaration increased fears that the world's second-largest economy will continue to sputter at a time when Chinese manufacturing growth is declining and European governments are struggling amid record deficits.

On the other hand, Hong Kong's Hang Seng ended the day at 19,471.8, down 0.13%, whereas the Shanghai composite index closed 0.12% up at 2,571.42.

The South Korean markets remained closed today.

In Europe, oil stocks dragged the markets after US started a criminal probe into Oil major BP's oil spill off the Gulf of Mexico.

The FTSE 100, UK's key index was ruling 1.63 percent lower at 5,079.07 points.

Its French peer, the CAC 40 was also in the negative at 3,447.08, down 1.6%, while the German DAX was trading with a 1.7% low at 5,879.31. (With Inputs from Agencies)