U.S. stocks plummeted Friday after reports of disappointing U.S. data added to the plunge in oil to below $30 a barrel and the sell-off in Chinese stocks which pointed to mounting concerns about the country’s slowdown.

The Dow (DIA) ended 391 points lower after earlier falling nearly 537 points. The S&P 500 (SPY) and Nasdaq (QQQ) indexes also lost more than 2 percent. The S&P 500 managed to stay above its August low of 1,867 in the close, briefly falling 3.5 percent in midday trade to its lowest since mid-October 2014.

According to Douglas Cote, chief market strategist at Voya Investment Management, “… some of [the drop in prices] was overselling. Still, (about) 400 points is pretty serious. I think … things could possibly get better.” Cote was advising investors to, “stick to global diversification and don’t panic.”

Friday marked an options expiration day that likely contributed to some volatility. U.S. stock markets will be closed Monday for Martin Luther King, Jr. Day and China GDP will be among the few data points from the country due out ahead of Tuesday’s U.S. trading session.

A “Mountain of Worry”

White House spokesman Josh Earnest said that despite the fact that the White House does not usually comment on market moves, market activity is being “closely watched at the Treasury Department” and that financial markets around the world are also under watch.

Ryan Larson, head of equity trading, U.S., RBC Global Asset Management (U.S.) Put it this way: “Simply put, we’re not talking about a wall of worry right now. We’re talking about a mountain.”