Stocks fell on Thursday after President Donald Trump said the U.S. will implement tariffs on steel and aluminum imports next week.

The Dow Jones industrial average closed 420.22 points lower at 24,608.98 after rising more than 150 points earlier in the day. The 30-stock index fell as much as 586 points.

The declined 1.4 percent to end at 2,677.67 — erasing its year-to-date gains — with industrials as the worst-performing sector. It also briefly broke below its 100-day moving average, a key technical level. The Nasdaq composite fell 1.3 percent to 7,180.56 and dipped below its 50-day moving average.

The U.S. will set tariffs of 25 percent for steel and 10 percent for aluminum, the president said. It is unclear whether they will apply to all imports or only metals from certain countries.

"That could really spook the market," said Marc Chaikin, CEO of Chaikin Analytics. "The biggest wildcard would be a trade war and nobody should be excited for that." Chaikin also noted some of the pressure seen in stocks is in response to the news on tariffs.

Shares of Ford Motor dropped 3 percent and General Motors fell nearly 4 percent. Boeing, Cummins, Johnson Controls and United Technologies — other users of steel and aluminum — also helped lead the market lower. Steel stocks like U.S. Steel and AK Steel posted strong gains.

Wall Street also digested fresh testimony from Federal Reserve Chair Jerome Powell. Powell spoke before the Senate Finance Committee later on Thursday.

After delivering prepared remarks, he said: "We don't see any strong evidence yet of a decisive move up in wages. We see wages, by a couple measures, trending up a little bit, but most of them continuing to grow at about two and a half percent. Nothing in that suggests to me that wage inflation is at a point of acceleration."

The Dow, S&P 500 and Nasdaq all hit session highs on the back of that comment before retreating. Earlier this week, he testified before the House Financial Services Committee, where he indicated market volatility won't stop the central bank from raising rates.