The Sensex and Nifty fell for a fourth straight session on Thursday, led by losses in financials and auto stocks, with Tata Motors weighing on the indexes after its first-quarter results failed to meet expectations.

At 11.45 a.m., the 30-share BSE index Sensex was down 98.03 points or 0.31 per cent at 31,699.81 and the 50-share NSE index Nifty was down 29.35 points or 0.3 per cent at 9,878.70.

Among BSE sectoral indices, auto index plunged 1.94 per cent, followed by power 1.24 per cent, capital goods 0.98 per cent and infrastructure 0.83 per cent.On the other hand, IT index was up 0.62 per cent, TECk 0.43 per cent, metal 0.33 per cent and realty 0.12 per cent.

Top five Sensex losers were Tata Motors (-6.74%), Sun Pharma (-1.63%), ONGC (-1.24%), NTPC (-1.21%) and Bajaj Auto (-1.17%), while the major gainers were Infosys (+1.46%), Tata Steel (+1.31%), Hero MotoCorp (+1.28%), Lupin (+0.88%) and Dr Reddy's (+0.85%).

The Nifty Auto index fell as much as 2.2 percent, its biggest percentage loss in over two-and-a-half months. Tata Motors, Eicher Motors and Motherson Sumi Systems pulled the index down, which has risen about 20 percent this year as of Wednesday's close.

The automaker's shares fell as much as 7.2 per cent to their lowest in over a year after the company's 42 per cent rise in June-quarter profit, helped by a one-off gain related to changes to Jaguar Land Rover's pension plans, failed to please investors.

Financial stocks continued their decline, with the Nifty Bank index dipping 0.5 percent and the Nifty PSU bank index losing as much as 1.9 percent.

Nifty Pharma index snapped its six-day losing streak after Aurobindo Pharma's first-quarter performance and management commentary boosted sentiment. The drugmaker's shares rose as much as 5.9 per cent.

Global sentiment was largely weak with Asian stocks falling as investors fretted about the simmering tensions between the United States and North Korea.