Equity benchmark Sensex tumbled over 850 points in the opening session on Friday, tracking a weak trend in global markets amid escalating tensions between Russia and Ukraine.

The 30-share Sensex slumped 851.99 points to 54,250.69 in early trade after a weak start. The broader Nifty declined 185.60 points to 16,312.45.

"Volatility in US equities continue as the Russian invasion of Ukraine entered its second week. Investors remain wary and attempt to gauge how international sanctions could penalise Putin's regime. The Dow Jones fell 0.3 per cent. The Nasdaq was down more than 1.6 per cent while the S&P 500 lost 0.5 per cent," according to Mitul Shah, Head of Research at Reliance Securities.

Asian Paints, Maruti Suzuki India, Axis Bank, Wipro and Mahindra & Mahindra were the biggest drag in morning trade, tumbling up to 4.51 per cent.

In the previous session, the 30-share BSE index finished 366.22 points or 0.66 per cent lower at 55,102.68. Similarly, the broader NSE Nifty declined 107.90 points or 0.65 per cent to close at 16,498.05.

Bourses in Hong Kong, Shanghai and Tokyo were trading significantly lower in mid-session deals.

Stock exchanges in the US closed in the negative zone in the overnight session.

Meanwhile, international oil benchmark Brent crude surged 1.53 per cent to USD 112.16 per barrel.

Foreign institutional investors continued their selling spree in Indian markets as they offloaded shares worth Rs 6,644.65 crore on a net basis on Thursday, according to exchange data.

"The war and surge in crude have completely transformed the economic scenario and market expectations. If the war prolongs global economic growth may be impacted," said V K Vijayakumar, Chief Investment Strategist at Geojit Financial Services.