In a volatile session, the S&P 500 came within a hair of its 200-day moving average, a key technical level. The benchmark index also nudged closer to its February low, which marked a correction, ending 9.9 percent lower than its Jan. 26 record.

“There is concern what the trade war could look like. Investors want to manage their risk. If it escalates rapidly, it could be a major headwind for the market,” said Peter Kenny, senior market strategist at Global Markets Advisory Group, in New York.

President Donald Trump’s plans for tariffs on up to $60 billion in Chinese goods moved the world’s two largest economies closer to a trade war as China declared plans to levy duties on up to $3 billion of U.S. imports including fruit and wine even as it urged the United States to “pull back from the brink.”

The Dow Jones Industrial Average .DJI fell 424.69 points, or 1.77 percent, to 23,533.2, the S&P 500 .SPX lost 55.43 points, or 2.10 percent, to 2,588.26 after hitting an intraday low that was barely above its 200-day moving average of 2585.22.

The Nasdaq Composite .IXIC dropped 174.01 points, or 2.43 percent, to 6,992.67.

For the week, the Dow was down 5.67 percent, the S&P 500 was down 5.95 percent and the Nasdaq was down 6.54 percent, marking their biggest weekly percentage falls since January 2016.

The Dow was down 11.6 percent since its Jan. 26 high, and hit its lowest close since confirming a correction in February.

The Cboe Volatility Index .VIX, the most widely followed barometer of expected near-term volatility in the S&P 500, finished up 1.53 points at 24.87, its highest close since Feb. 13.

The S&P’s financial sector .SPSY was the S&P’s biggest percentage loser, at 3 percent, after a volatile session in which it was whip-sawed by volatile Treasury yields.

Bloomberg News cited China’s ambassador to the United States saying that the country is “looking at all options” in response to tariffs, which could include scaling back purchases of U.S. Treasuries.

Nasdaq was weighed down by declines in momentum stocks such as Facebook (FB.O), Amazon.com (AMZN.O), Microsoft (MSFT.O) and Google’s parent Alphabet (GOOGL.O).

The semiconductor sector took a fall after Micron Technology’s (MU.O) quarterly report stoked fears about falling NAND prices. The Philadelphia Semiconductor index .SOX slumped 3.3 percent.

Declining issues outnumbered advancing ones on the NYSE by a 3.96-to-1 ratio; on Nasdaq, a 3.72-to-1 ratio favored decliners.

The S&P 500 posted two new 52-week highs and 42 new lows; the Nasdaq Composite recorded 23 new highs and 93 new lows.

Volume on U.S. exchanges was 8.11 billion shares, above the 7.3 billion average for the last 20 trading days.