Markets already were cautious in advance of this week's Federal Reserve meeting, which is expected to produce another rate hike, following Friday's sell-off on worries about slowing global growth.

About 15 minutes into the day's trading, the benchmark Dow Jones Industrial Average declined 1.1 percent at 23,838.93 while the broader S&P 500 also fell 1.1 percent to 2,571.58.

The Nasdaq dropped 1.3 percent to 6,820.59, wiping out all its gains for 2018.

President Donald Trump added to the air of unpredictability before markets opened, lashing out at the Fed on Twitter over its plans to raise interest rates at a two-day meeting due to begin Tuesday.

Meanwhile, a regional survey showed manufacturing activity in the New York region plunged this month, adding to the somber mood.

"There isn't a lot of mystery behind the negative bias. Trade uncertainty, political uncertainty, growth uncertainty and monetary policy uncertainty continue to provide a rationale to reduce risk exposure," analyst Patrick O'Hare wrote at Briefing.com

Investment bank Goldman Sachs fell 2.2 percent, extending losses after Malaysian authorities joined their American counterparts in bringing criminal charges over the long-running 1MDB fraud scandal.