Stocks tank over outbreak fears.

Stocks fell sharply on Wall Street Friday as fears spread through the markets that a virus outbreak emanating from China will dent global growth.

The Dow Jones Industrial Average skidded more than 600 points and the S&P 500 index erased its gains for January.

Technology companies, which do a lot of business with China, led the losses. Airlines fell after Delta and American suspended flights to and from the country.

Just two weeks ago, the S&P 500 had closed at an all-time high, having climbed around 13% since early October. A preliminary trade deal signed by the U.S. and China earlier in the month eased a big source of uncertainty in the markets. Volatility was running at 12-month lows and even a dust-up between the U.S. and Iran didn’t rock markets.

Then came the virus outbreak. Markets around the globe have sold off on concerns about the potential economic impact of the outbreak.

Economists are scrambling to calculate the virus’ impact on China’s economy. The Chinese economy is far bigger and more closely integrated with the rest of the world than it was at the time of the SARS outbreak 17 years ago. China now accounts for 16% of global economic output, up from 4% in 2003.

Ben May, director of global macro research at Oxford Economics, estimates that the virus will shave 0.4 percentage points off Chinese economic growth this year, leaving it at 5.6%, the slowest since 1990, and reduce global growth by 0.2 percentage points to 2.3%, the weakest since the financial crisis.

Others expect a repeat of the SARS experience: a quarter or two of weaker Chinese growth followed by a quick and full recovery with limited fallout worldwide.

“History suggests that unless the end of the world is going to be caused by this flu-like virus, it will prove to be only a slight headwind for the global economy,’ Carl Weinberg, chief economist at High Frequency Economics, wrote in a research report.