Continuous FIIs' selling along with caution over the rising Omicron variant cases triggered a massive slide in key domestic equity indices on Monday's post-noon trade session.

Notably, India VIX (volatility index) spiked to its nine days high levels and signified the dominance of the bears in the market.

Besides, all sectors traded in the negative territory out of which Realty, Banking and Financial counters witnessed the most weakness and selling pressure.

Consequently, at 12.45 p.m., the S&P BSE Sensex declined by 1,601.35 points or 2.81 per cent to 55,410.39 points.

Similarly, NSE Nifty50 fell by 527.25 points or 3.10 per cent to 16,457.95 points.

Initially, both the indices made a gap-down opening due to the rise in Omicron coronavirus cases worldwide.

Besides, traders were cautious with continuous net outflow of foreign funds.

The Foreign Portfolio Investors (FPIs) have pulled out Rs 17,696 crore from the Indian markets in December so far.

"Our research suggests that the levels of 16,350 may act as support levels in the market," said Gaurav Garg, Head of Research, CapitalVia Global Research.

"If the market is unable to sustain above the level of 16,350, we can expect the market to trade till the lower range of 16,000-16,100."

According to Chandan Taparia, Vice President, Equity Derivatives and Technical, Broking & Distribution, MOFSL: "Nifty opened gap down and witnessed sharp selling pressure which drooled it down to 16,539 levels."

"Market breadth continues to be deep in favour of the declining counters indicating weakness swept across the street."