A maverick senator from Donald Trump's own Republican party launched a stinging attack on the president on Wednesday, accusing him of employing Stalinist language to attack and undermine the free press.

Arizona lawmaker Jeff Flake levelled the broadside in an address from the Senate floor, timed to coincide with the expected announcement of controversial "Fake News Awards" by Trump's administration.

Flake -- an outspoken critic of the president who is not seeking re-election this year -- hit out at what he called Trump's disregard for the truth, and his repeated designation of the news media as an "enemy."

"The 'enemy of the people' was how the president of the United States called the free press in 2017," Flake told lawmakers.

"Mr. President, it is a testament to the condition of our democracy that our own president uses words infamously spoken by Joseph Stalin to describe his enemies," he said.

"So fraught with malice was the phrase 'enemy of the people,' that even Nikita Khrushchev forbade its use."

Flake accused Trump's White House of a "daily assault" on the constitutionally protected right to free speech, calling it "as unprecedented as it is unwarranted."

And he accused Trump of committing "moral vandalism" against the truth, from his longtime questioning of Barack Obama's birth certificate to his dismissal of Russian meddling in the 2016 election as a "hoax" -- and warned he was emboldening authoritarian regimes around the world to persecute the press.

"2017 was a year which saw the truth -- objective, empirical, evidence-based truth more battered and abused than any time in the history of our country, at the hands of the biggest figure in our government," Flake said.

"Without truth and a principled fidelity to truth and to shared facts, Mr President, our democracy will not last," he warned.

Trump tweeted last week that he would be awarding "Fake News Awards" to the "most corrupt & biased of the Mainstream Media" this Wednesday -- but the White House has remained evasive on whether the controversial event, already once delayed, would take place.