Washington DC - Social media was flooded with baseless claims of voter fraud in the final hours of the US presidential election – until Donald Trump claimed victory.

Allegations of "massive cheating" in the biggest city of the key state of Pennsylvania and images claiming to show discarded ballots in North Carolina are just some of the unfounded theories that spread on social media in the election's home stretch.

The former president never admitted defeat in the 2020 election, a denial that culminated with supporters of the ex-reality TV star violently attacking the US Capitol in a bid to block certification of the vote.

Despite weeks of claiming that this year's election was marred by widespread voting irregularities, the former president declared a "magnificent" victory and pledged to "heal" the country as he defeated Kamala Harris in a stunning White House comeback.

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Disinformation sowed doubt about the integrity of the voting process in several battleground states right up until the end, particularly in key swing states such as Pennsylvania.

False claims that voting machines were flipping votes from Trump to Harris and purported footage of non-citizens voting in Pennsylvania spread quickly, despite confirmation from experts that voter fraud in the US is incredibly rare.

In the hours before polls closed in Philadelphia, Trump claimed there was "a lot of talk about massive cheating" in Pennsylvania's soundly left-leaning city and said law enforcement was "coming."

A city official promptly denied the claim, calling it "yet another example of disinformation," while Philadelphia police and the district attorney's office rejected the unsubstantiated allegation.

Trump won the state's 19 electoral college votes – considered the biggest battleground prize in this year's vote – helping him reach the necessary minimum of 270 electoral votes.

Preying on an already tense political climate, those behind the disinformation stoked fears of physical violence, culminating in false bomb threats in scores of polling places that authorities have attributed to a Russian interference campaign.

In the swing state of Georgia, thousands shared an unfounded rumor of attacks by members of the racist Ku Klux Klan organization, raising concerns for voters heading to polling stations.

"Hateful discourse... aims to instill fear in the community and disrupt us from exercising our constitutional rights," the Gwinnett County Sheriff's Office, just outside the capital Atlanta, said in response to the rumor.

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Social media users also shared altered images, including one allegedly showing CNN broadcasting results in favor of Harris, that fuelled claims the race was rigged to benefit the Democratic candidate.

The screenshot rocketed across the Elon Musk-owned platform X, spreading widely in the so-called "Election Integrity Community" that the billionaire Trump cheerleader created to "share potential incidents of voter fraud or irregularities."

"This image is completely fabricated and manipulated and it never aired on any CNN platform," CNN's senior vice president of communications Emily Kuhn told AFP.