US President Donald Trump took a victory lap in a speech to Congress on Tuesday, exulting in a series of dramatic actions that have upended American foreign policy, ignited a trade war with close allies and slashed the federal workforce since he took office six weeks ago.

"To my fellow citizens, America is back," Trump began to a standing ovation from fellow Republicans.

"We have accomplished more in 43 days than most administrations accomplish in four years or eight years -- and we are just getting started," Trump said to frequent chants from loyal lawmakers of "USA, USA!"

"The American Dream is surging -- bigger and better than ever before. The American Dream is unstoppable, and our country is on the verge of a comeback the likes of which the world has never witnessed, and perhaps will never witness again."

The primetime speech, his first to Congress since taking office on January 20, capped a second day of market turmoil after he imposed sweeping new tariffs against Mexico, Canada and China.

Trump spoke in the House of Representatives, where lawmakers huddled in fear for their lives a little over four years ago while a mob of Trump supporters ransacked the Capitol in an unsuccessful effort to overturn Joe Biden's 2020 victory over the then-incumbent Trump.

The president called his first few weeks in office "the most successful" first month of any US presidency in history.

He will also defended his tariff campaign, despite concerns that it could raise consumer prices and slow economic growth.

"Whatever they tariff us, we tariff them. Whatever they tax us, we tax them," Trump said.

"If they do non-monetary tariffs to keep us out of their market, then we do non-monetary barriers to keep them out of our market."

World leaders were watching Trump's speech closely, a day after he paused all military aid to Ukraine.

The suspension followed an Oval Office blowup in which Trump angrily upbraided Ukrainian President Volodymyr Zelensky in front of TV cameras.

The pause in aid threatened Kyiv's efforts to defend against Russia, and further rattled European leaders worried that Trump is moving the US too far toward Moscow.

Trump's 25 percent tariffs on Mexico and Canada, two of the country's closest allies, and an additional 10 percent on Chinese imports deepened investor concerns about the economy.

The Nasdaq Composite is down more than nine percent from its record closing high on December 16. (Agencies)