Thousands of die-hard Donald Trump supporters rallied for a last stand Saturday in Washington, chanting "four more years" and blaming fraud for an election defeat that will force the president to vacate the White House after just one term.

Trump himself made a drive-past in his armoured motorcade, on his way to play golf, smiling through his limousine window to wild cheers and signs saying "Best prez ever" and "Trump 2020: Keep America Great."

The Republican incumbent is sticking to discredited claims of mass fraud and claiming he defeated President-elect Joe Biden in the November 3 vote, marking another unprecedented challenge to US democratic norms as his time in office runs down.

At least 10,000 people -- few wearing masks -- massed on the city's Freedom Plaza before marching towards the Supreme Court, brandishing flags in a raucous atmosphere reminiscent of a Trump campaign rally.

"President Trump deserves to see who's behind him, he deserves to feel the love," marcher Kris Napolitana, from Baltimore, told AFP. "I believe that he's going to win when all the fraud and cheating is found out."

With right-wing militia group the Proud Boys also among those attending, a large security presence was deployed to prevent clashes with anti-Trump events outside the Supreme Court.

- 'Whole system's rigged' - 

The latest tallies gave the Democrat Biden a clear win in the state-by-state Electoral College that decides the presidency, with 306 votes against Trump's 232. Two hundred seventy votes are required for election.

But Margarita Urtubey, 49, a horse breeder who flew in from Miami with her sister, said the election was "so corrupt," adding "Trump won by a landslide. We are here to march for the 'stop the steal' of this election, to make our voice heard."

With the march underway, Trump tweeted that "hundreds of thousands" had turned out -- while his spokeswoman Kayleigh McEnany made the greatly exaggerated claim that more than a million people were present.

But the turnout was undoubtedly high for a strongly Democratic city, boosted by protesters from around the country, from Florida to Pennsylvania or Colorado.

Darion Schaublin drove from Columbus, Ohio to protest the fact "the whole system's rigged... in the way that the information is getting to the people."

"The truth never actually gets out," said the 26-year-old, who says he lost his job in a restaurant after refusing to wear a mask as protection from Covid-19.

President Trump is impeding Biden's transition ahead of inauguration on January 20 and has filed numerous lawsuits -- unsuccessfully -- to challenge vote counts around the country.

Trump said Friday that "time will tell" if he remains president, in a momentary slip of his refusal to concede his election defeat.

The hint of doubt came despite him continuing to claim that mass fraud -- for which no evidence has been produced -- robbed him of victory.

- Biden prepares for power -

Despite his own intelligence officials' declaration this week that the election was "the most secure in American history," Trump and his right-wing media allies show no sign of giving up their quest to get the results overturned.

After driving past the marchers in Washington, Trump headed to his golf club outside the capital on his regular weekend routine.

Half a dozen supporters stood at one side of the entrance with Trump flags, and about the same number stood on the opposite side with a big "Biden Harris" sign and one that said: "We voted. You're fired."

Biden on Saturday went biking in a Delaware state park with his wife Jill and a security detail. When asked if he was closer to choosing his cabinet, he replied "yes."

Despite Trump's stance, the president-elect is preparing for power, with many world leaders acknowledging his victory.

China was the latest nation on board, with a foreign ministry spokesman saying, "We express our congratulations."