January 21, 2020 - President Donald Trump on Tuesday lashed out at the "perennial prophets of doom" who warn that the world is in the throes of a major environmental crisis, as he addressed an audience in Davos including Swedish teenage campaigner Greta Thunberg.

"We must reject the perennial prophets of doom and their predictions of the apocalypse," Trump said, hours after Thunberg told the World Economic Forum that governments had done "basically nothing" to reverse climate change.

Much of Trump's speech revolved around the success of the US economy.

He reminded the audience that when he spoke there two years ago, early in his presidency, "I told you that we had launched the great American comeback".

"Today I'm proud to declare the United States is in the midst of an economic boom, the likes of which the world has never seen before," the president said.

Trump's participation in the annual gathering of political and business elites in the Alpine ski resort will provide a conspicuous split-screen moment in a presidency familiar with them.

The two-day Swiss visit will test Trump's ability to balance his anger over being impeached with a desire to project leadership on the world stage.

Speculation had mounted that Trump would cancel the trip due to the Senate trial, but aides said he remains focused on producing results for the American people.

"America is thriving. America is flourishing and yes, America is winning again like never before," Trump said before talking about a newly-signed trade deal with China and a pending trade agreement with Mexico and Canada.

Trump also spoke of record low unemployment, stock market gains and millions removed from unemployment.

He planned to meet with world leaders and business executives after the speech.

Swooping in for his second appearance at the conference, Trump was set to depart on Wednesday, jetting back to Washington, which is consumed by the impeachment trial.

Trump denies any wrongdoing and argues that Democrats want to remove him from office because they know they can't deny him re-election in November.

He would be forced to leave office if convicted, but the Republican-controlled Senate is expected to acquit him.

Donald Trump arrives on Marine One at the heliport in Davos.

Photo: AAP

President Donald Trump at the World Economic Forum on Tuesday.

Photo: AAP

Swedish environmental activist Greta Thunberg listens to Donald Trump.

Photo: AAP