Traders said cutting down on bets by cautious participants in view of expiry of February derivatives contracts kept sentiment fragile.
The 50-share Nifty tumbled to 6,997.40, down 21.30 points, or 0.30 per cent, at 1354 hours.
Railway Minister Suresh Prabhu today proposed increasing capital outlay for the Railways, the world's fourth-largest rail network, by 21 per cent to Rs 1.21 lakh crore.
The 30-share Sensex started higher at 23,105.16 and hovered in a range of 23,142.96 and 22,990.53 before quoting at 23,006.63 at 1354 hours, a loss of 82.30 points, or 0.36 per cent.
Among major indices, IT dropped 1.19 per cent followed by utilities 1.87 per cent, power 1.33 per cent and technology 1.10 per cent.
Meanwhile, foreign portfolio investors (FPIs) sold shares worth net Rs 730.99 crore yesterday, provisional data from the stock exchanges showed.