Equity benchmark Sensex crashed about 870 points to slip below the 55,000-level in opening deals on Monday in line with weakening global sentiments amid the worsening Russia-Ukraine crisis.

The 30-share BSE Sensex was trading 869.33 points or 1.56 per cent lower at 54,989.19 in early trade and the NSE Nifty plunged 233.80 points or 1.40 per cent to 16,424.60.

Barring PowerGrid, Tata Steel and Sun Pharma, all Sensex shares were trading in the red.

Snapping its seven-day losing streak on Friday, the 30-share BSE Sensex had climbed 1,328.61 points or 2.44 per cent to settle at 55,858.52. Similarly, the broader NSE Nifty had soared 410.45 points or 2.53 per cent to 16,658.40.

On a weekly basis, the Sensex had lost 1,974 points or 3.41 per cent and the Nifty gave up 618 points or 3.57 per cent.

Meanwhile, in a dramatic escalation of tensions in eastern Europe, Russian President Vladimir Putin ordered his nuclear forces to be on high alert in response to what he called "aggressive statements" by leading NATO powers over the Ukraine conflict.

Spooked by the Ukraine crisis, foreign institutional investors further offloaded shares worth Rs 4,470.70 crore in the Indian capital markets on Friday, exchange data showed.

Asian shares were trading mostly lower in afternoon trade on Monday, tracking the worsening geopolitical crisis in eastern Europe.

Oil prices, which have been rising since the Russian invasion on Ukraine, shot up again on Monday on worries about supply disruptions. Brent crude futures were up over 5 per cent at USD 99.61 a barrel.