Supporters of US President Donald Trump wave a Betsy Ross flag with a circle of 13 five-point stars representing the 13 original colonies during a protest in Washington DC on Saturday. Photo: AFP

Thousands of red-hatted protesters filled Washington DC's streets Saturday to support US President Donald Trump's baseless claims of election fraud, undeterred by the US Supreme Court's rejection of what may have been his last chance to overturn the results.

Thousands gathered around Freedom Plaza, a few blocks from the White House, in a festive atmosphere earlier in the day, while scuffles broke out later between protesters and counter-demonstrators.

Police used their bodies and bicycles to keep the groups apart. There was also at least one clash between police and counter-protesters.

Six people were arrested, following five arrests Friday night related to a brawl, local media reported.

Some pro-Trump demonstrators showed up in tactical gear, chanting "USA" and "four more years" for the outgoing president.

It was a sizable crowd, but noticeably smaller than a similar rally in November when 10,000 people converged near the White House to support Trump.

"We're not gonna give up," said Luke Wilson, a 60-something protester who had come all the way from the western State of Idaho.

Protesters offered no shortage of explanations for the results of the November 3 election won by Democrat Joe Biden, even though it has been affirmed by state election officials - several of them Republican - and by judges in several key states.

Every state has now certified Biden's victory, giving the Democrat 306 votes in the Electoral College to Trump's 232, with 270 required for election. 

But protesters insisted, as Trump has repeatedly done, that there was widespread fraud in the election.

Some pointed to "foreign interference," others to software that allegedly erased millions of votes for the president - but not those for other Republican candidates on the same ballots. 

Susan Bowman, a 62-year-old from Hampton, Virginia, said "this is not a banana republic. We need to fix the election."

AFP