Stocks were sharply lower on Thursday as investors fled to safe-haven assets in the face of global uncertainty.

The S&P 500 was down 1.8%, the Dow Jones Industrial Average fell 1.8%, and the Nasdaq slid 1.5%.

Global central banks took center focus on Thursday with many investors skeptical that officials can rein in rampant volatility and soothe financial markets. Sweden's central bank cut its main interest rate further below zero, an aggressive move that spooked European investors worried over the extent of a financial downturn. 

Meanwhile, the safe-haven yen saw its strongest gains since the downfall of Lehman Brothers in 2008, undercutting the Bank of Japan's late-January efforts to tamp down currency inflation by turning interest rates negative. 

The U.S. central bank was in the spotlight, too, after Federal Reserve Chair Janet Yellen conceded there is chance of recession in any year, though didn't make a judgement on whether the U.S. economy is headed that way. Yellen told the Senate banking committee the Fed will make an assessment of the economy at its March meeting.

Yellen testified to the House Financial Services Committee on Wednesday, assuring members that future rate hikes would be gradual. She also noted that the U.S. is vulnerable to a number of challenges, including a stronger dollar and weaker commodities prices.

Crude oil entered another tailspin on Thursday morning, dumping around a dollar a barrel over concerns of weaker demand and what it spells for the global economy. Commodity traders have also shown concern over a supply glut and the inability of some of the largest oil-producing countries to address it. West Texas Intermediate crude oil fell 1.2% to $27.11 a barrel.

Safe-haven assets such as gold jumped as investors fled riskier equities markets. Gold climbed by its most in a year, up 2.5% to $1,227.50 an ounce. Gold is up for its ninth time in 10 days.

The labor market continued to show strength with weekly jobless claims falling to their lowest level since mid-December. The number of new claims for unemployment benefits dropped by 16,000 to 269,000. The four-week average, a less volatile measure, fell 3,500 to 281,250.

Twitter (TWTR - Get Report) slumped 3% on fears of slowing user growth. The social network reported that 305 million users signed into the service at least once a month, up 6% from a year earlier, marking its slowest year-over-year growth ever.

"We are clearly disappointed with the company's failure to grow its user base at a very critical point in its history," wrote TheStreet's Jim Cramer, whose Action Alerts PLUS charitable trust portfolio includes Twitter stock. "The bottom line: The market cares about user growth and Twitter hasn't proven its ability to deliver. We reiterate that the stock will remain pressured until this changes."

Exclusive Look Inside: Want to be alerted before Jim Cramer buys or sells TWTR? Learn more now.

Cisco (CSCO - Get Report) jumped 8% in after beating analysts' earnings estimates in its recent quarter and boosting its dividend. The networking tech company raised its dividend by 24% to 26 cents a share and authorized an additional $15 billion in share buybacks.

Cisco is a holding in Jim Cramer's Action Alerts PLUS charitable trust portfolio.

Whole Foods (WFM) shares were up 1.4% after the supermarket chain reported a better-than-expected quarter. Same-store sales decreased 1.8% on a constant-currency basis in its first quarter, a slower decline than an expected 2.1% drop. Whole Foods expects sales growth of at least 3% in fiscal 2016.

Mylan (MYL - Get Report) fell 16% after agreeing to buy Swedish drugmaker Meda Aktiebolag in a deal worth $7.2 billion, or $9.9 billion including debt. Shares were also lower after the pharmaceuticals company reported disappointing full-year 2015 results.

Tesla (TSLA - Get Report) rocketed 11% higher after guiding for an upbeat quarter. The automaker expects to deliver 16,000 vehicles in the current quarter, up 60% from a year earlier. Tesla expects to deliver between 80,000 and 90,000 units for the full year.'s (AMZN - Get Report) board approved the repurchase of up to $5 billion of the company's stock. The stock buyback, which doesn't have a fixed expiration, replaces the $2 billion stock repurchase program approved by the board in 2010. Shares were down 1.3%.