Wall Street traders were back in sell-off mode Wednesday while the dollar fell further as downcast comments from Federal Reserve Chair Jerome Powell added to weakness in semiconductor giant Nvidia.

After a relatively peaceful couple of days on markets following tariff-related volatility last week, investors were once again on the defensive. Gold, a safe-haven asset in times of uncertainty, climbed above $3,300 an ounce for the first time.

US equities opened lower, shrugging off solid retail sales data. But the market dropped much more after Powell warned that Trump's tariffs could put the Federal Reserve in the unenviable position of having to choose between tackling inflation and unemployment.

Powell said that while the Fed's employment and inflation goals were largely in balance at this point, policymakers could find themselves in the "challenging scenario" depending on how things evolve.

"Tariffs are highly likely to generate at least a temporary rise in inflation," Powell told the Economic Club of Chicago, warning that the inflationary effects "could also be more persistent."

US stocks hit session lows shortly after Powell's comments before recovering a bit in the final minutes of trading.

The Nasdaq finished down more than three percent.

Nvidia ended down around seven percent after earlier slumping more than 10 percent. The chip company disclosed in a securities filing that it expects a $5.5 billion hit connected to export licenses for technology that the US government determined could be used for a Chinese supercomputer.

Powell's comments "sparked stagflation concerns," said Jack Ablin of Cresset Capital. 

Powell "took what was a moderately down day into a pretty dramatic slide," Ablin added.

The dollar also weakened further after Powell's remarks, retreating about one percent against the euro.

"Markets are increasingly convinced that the US economy is losing steam," said a comment from Forexlive published ahead of Powell's remarks that pointed to market speculation about Fed interest rate cuts.

The battering on Wall Street followed a mixed session in Europe.

London's benchmark FTSE 100 stock index closed 0.3 percent higher, as official data showed UK inflation slowed more than expected in March.

Frankfurt also finished 0.3 percent in the green while Paris fell almost 0.1 percent.

Last week Trump backed off his most onerous "reciprocal" tariffs for every country except China, while maintaining a range of other levies, including on car imports. 

There has been little sign of rapprochement between Washington and Beijing, which has responded with increased levies of its own. 

"Markets continue to suffer from the White House's tariff flip-flopping," said City Index and Forex.com market analyst Fawad Razaqzada.

"The stop-start nature of US trade policy this month has made long-term positioning something of a fool's errand, with volatility dominating the landscape."

Key figures at 2050 GMT

New York - Dow: DOWN 1.7 percent at 39,669.39 (close)

New York - S&P 500: DOWN 2.2 percent at 5,275.70 (close)

New York - Nasdaq: DOWN 3.1 percent at 16,307.16 (close)

London - FTSE 100: UP 0.3 percent at 8,275.60 (close)

Paris - CAC 40: DOWN 0.1 percent at 7,329.97 (close)

Frankfurt - DAX: UP 0.3 percent at 21,311.02 (close)

Tokyo - Nikkei 225: DOWN 1.0 percent at 33,920.40 (close)

Hong Kong - Hang Seng Index: DOWN 1.9 percent at 21,056.98 (close)

Shanghai - Composite: UP 0.3 percent at 3,276.00 (close)

Euro/dollar: UP at $1.1395 from $1.1282 on Tuesday

Pound/dollar: UP at $1.3235 from $1.3231

Dollar/yen: DOWN at 142.12 yen from 143.21 yen 

Euro/pound: UP at 86.06 pence from 85.26 pence

Brent North Sea Crude: UP 1.8 percent at $65.85 per barrel

West Texas Intermediate: UP 1.9 percent at $62.47 per barrel