Opponents of US President Donald Trump belittled his order to put on a massive military parade in Washington DC to celebrate American power with one calling him "Napoleon in the making".

Trump's order to his generals to prepare a military extravaganza replete with tanks and marching soldiers was met with comparisons on Wednesday to autocratic displays that occur in nations such as China, North Korea, and previously the Soviet Union.

"I don't think anyone believes this would be about trying to honour men and women who serve our country," DC Council member Charles Allen told the Washington Post. "This would only be about feeding one man's ego."

Democratic Congressman Keith Ellison described Trump's order as "the Exalted Leader's latest idiot [and authoritarian] idea".

"We have a Napoleon in the making here," said Congresswoman Jackie Speier.

'Kind of cheesy'

The idea for the show of military might apparently came after Trump visited France last July for Bastille Day when an impressive military display was held.

Sitting on the Champs-Elysees, Trump marvelled at the Republican Guard on horseback as fighter jets flew overhead and President Emmanuel Macron arrived in a camouflaged military jeep.

"So we're actually thinking about Fourth of July, Pennsylvania Avenue, having a really great parade to show our military strength," Trump said months after his Paris experience.

Such shows of force are rare in the United States. The last major parade in Washington took place in 1991, after the Gulf War. It cost more than $8m, which would be significantly more in today’s dollars.

"It's a fantastic waste of money to amuse the president," said Democratic Senator Dick Durbin.

Even Trump's supporters were lukewarm to the idea.

Republican Senator Lyndsey Graham told reporters on Capitol Hill on Wednesday a parade "makes sense". But he added: "I'm not looking for a Soviet-style hardware display. That's not who we are, it's kind of cheesy, and I think shows weakness quite frankly."

'Cadet Bone Spurs'

Trump has frequently touted his support for the US military and placed high-ranking generals in top White House and cabinet posts.

Press Secretary Sarah Sanders said Trump's intention was to have "a celebration" of the military.

Trump already raised fears over growing authoritarianism earlier this week after calling Democrats who did not applaud his State of the Union address "un-American" and "treasonous". The White House said the president was "clearly joking".

Military veteran and Democratic Senator Tammy Duckworth - who lost both legs fighting in Iraq - denounced Trump's comments. She noted medical deferments for a foot ailment meant he didn't have to serve in the Vietnam War.

"We don't live in a dictatorship or a monarchy," said Duckworth.

"I swore an oath - in the military and in the Senate - to preserve, protect and defend the constitution of the United States, not to mindlessly cater to the whims of 'Cadet Bone Spurs' and clap when he demands I clap."