The rally comes more than a week after The Associated Press and other major news outlets projected Joe Biden had won the election, securing at least 290 electoral college votes.
Biden is also projected to have won the popular vote, garnering 5.3 million more votes than Trump.
The “Million MAGA March” rally was scheduled to begin at 12 p.m. ET, but by 10:30 a.m., a large crowd had already gathered.
The demonstrations took place in Washington and in other cities, and featured a mix of the president’s backers, far-right personalities and members of the Oath Keepers militia and Proud Boys in a public display of support for his effort to stay in power.
Meanwhile, some left-wing groups planned counter-demonstrations in Washington and elsewhere.
A Washington Post report said the president drove down Pennsylvania Avenue in his motorcade just after 10 a.m. to greet his supporters.
Video showed marchers rush towards the motorcade as Trump smiled and gave a thumbs up to his supporters.
A day earlier, Trump tweeted saying he intended to “stop by and say hello,” before repeating false claims that the “election was rigged.”
Twitter has placed a warning on the post, saying “this claim about election fraud is disputed.”
Just hours later after Trump’s drive-by around the city, clashes between pro-Trump demonstrators began to erupt across the capital city, with videos on social media showing projectiles being thrown and fistfights on the streets.
According to The Associated Press, city officials said at least 20 people were arrested by police on several charges, including assault and weapons possession.
In a tweet Saturday night, Trump told the D.C. police to “get going” and to “do your job and don’t hold back,” while pinning the blame on Antifa for starting the street clashes.
“ANTIFA SCUM ran for the hills today when they tried attacking the people at the Trump Rally, because those people aggressively fought back,” read Trump’s tweet.
In the days following the election, Trump has repeated these claims –without providing evidence — alleging that there was mass voter fraud as a result of the wide-scale use of mail-in ballots due to the novel coronavirus pandemic.
The Trump team has filed a number of lawsuits in key battleground states, alleging that Republican officials were not granted access to oversee ballot counting, while other suits claim ballots arriving after election day are fraudulent and should not have been counted.
However, election officials across the country have maintained that there was no fraud or evidence of irregularities.
On Friday, judges in the swing states of Arizona, Michigan and Pennsylvania all dismissed court challenges aimed at overturning the results of the vote.
And the Department of Homeland Security has declared the Nov. 3 election to be the most secure in U.S. history, finding no evidence of electoral fraud.
Meanwhile, Biden and Vice President-elect Harris have wasted no time in preparing their transition team.
On Monday, Biden announced members of his coronavirus task force.
The group will be led by former Surgeon General Dr. Vivek Murthy, former Food and Drug Administration Commissioner David Kessler and Yale University public health care expert Dr. Marcella Nunez-Smith.
The president-elect is also reportedly planning on appointing a woman to lead the Pentagon.
–With files from Reuters and The Associated Press and Global News’ David Lao