US President Donald Trump's tariffs risk higher unemployment and will likely cause inflation to rise and growth to slow, Federal Reserve Chair Jerome Powell said on Friday.

Trump's dramatic trade measures announced earlier this week have tightened scrutiny of Powell and how the Fed will react to free falling financial markets and concerns that a prolonged trade war would ramp up consumer prices and joblessness rates.

"The same is likely to be true of the economic effects, which will include higher inflation and slower growth," Powell told an event in Virginia., adding that it was "too soon" to consider changes to US monetary policy.

Powell spoke just minutes after Trump posted on social media, urging him to cut interest rates immediately and accusing him of playing politics in his role running the independent US central bank.

The larger-than-expected tariffs unveiled on Wednesday stack on top of earlier country-specific levies, meaning that China, for example, will now face a new levy totalling 54 percent.

Other top trading partners will also see higher rates, with the European Union now facing a 20 percent tariff from April 9, and India looking at a 26 percent levy.

The Trump administration has also targeted specific sectors of the economy, recently slapping a 25 percent tariff on automobiles not made in the United States.

Powell said Friday that he expected the current uncertainty to decline in the coming months.

Powell's comments suggest the Fed is in no rush to cut its benchmark lending rate from its current elevated level of between 4.25 and 4.50 percent, as it continues its struggle to bring inflation down to its long-term two percent target.

In recent months, the Fed's progress in bringing inflation down to target has stalled, while growth has remained solid and the unemployment rate has hugged close to historic lows.

Faced with this data, the Fed voted last month to extend its pause in rate cuts and signalled that it wanted to see how the new administration's policies would feed through to the economy before taking any action.

Fed policymakers - now including Powell - have warned that tariffs could cause prices to rise, with the extent of the price increase likely determined by the rollout of the levies and how consumers and businesses respond.

Ahead of Powell's speech on Friday, Donald Trump took to his Truth Social account to insist that his tariff policy would not change despite the market reaction and called on Powell to act.

"CUT INTEREST RATES, JEROME, AND STOP PLAYING POLITICS!" wrote Trump, who first nominated Powell to run the Fed, before turning against him during his first term.

Speaking Friday, Powell insisted he had no plans to step down as Fed chair before his term ends next year. "I fully intend to serve all of my term," he said during the Virginia event. (AFP)