US equity indexes whipsawed Monday, with volatility soaring to the second-highest since the 1990s, as investors tackled rumors and threats of more tariffs on China.

The Nasdaq fell 1.7% to 15,320.4 in midday trading on Monday, after touching an intraday low of 14,784.03. The S&P 500 dropped 1.9% to 4,975.9, following a decline to 4,835.04 earlier in the session. Similarly, the Dow Jones Industrial Average traded 2.5% lower to 37,363.1 after touching a low of 36,611.78 in the morning session. All three indexes touched a 52-week low intraday, with the S&P 500 reportedly heading for bear market territory.

All sectors, except communication services, declined in midday trading, with real estate and materials emerging as the steepest decliners.

The CBOE Volatility Index jumped 10.5% to 50.07 intraday, which is second-highest only to the level seen in 2020. The current level of volatility is above the peak scaled during the global financial crisis.

President Donald Trump reportedly said Monday that he plans to impose an additional 50% tariff on China if the world's second-largest economy fails to withdraw the retaliatory tariff it had announced last week on the US. "Additionally, all talks with China concerning their requested meetings with us will be terminated!" he wrote in a message on Truth Social.

The White House, meanwhile, told CNBC that any talk of a 90-day pause in implementing tariffs on all countries except China was "fake news."

Almost all US Treasury yields rose intraday, with the 10-year yield up 12.2 basis points to 4.11% and the two-year rate 3.5 basis points higher at 3.71%.

West Texas Intermediate crude oil futures dropped 2.2% to $60.56 a barrel.