Washington (AFP) - A gush of misinformation around US midterm elections could turn into a torrent after voting ends, experts warn, as tensions grow around key razor-tight races.

Some results are not expected to be declared for days or weeks, a delay that could trigger what observers fear will be a flood of bitter challenges and unfounded claims of election malpractice.

Far-right Republican candidates -– who endorse former president Donald Trump’s baseless claim that the 2020 election was stolen from him –- have already seized on isolated voting machine glitches to launch what many saw as preemptive efforts to discredit the results.

“After election night, the focus will narrow,” the Election Integrity Partnership (EIP), a non-partisan research group, said in a report.

“As the public wakes up on Wednesday… to find some races still in play and some races in which their candidate unexpectedly lost, partisans will swing their attention to the rumors most relevant to those races, seeking to amplify them and spin them into larger stories.”

The main focus is on the tight races in battleground states – including Georgia, Pennsylvania, Nevada and Arizona -– with a single seat enough to swing control of the Senate.

“If we have close elections, particularly if they involve party control of the US Senate, disinformation will get worse,” Rick Hasen, a professor and director of the “Safeguarding Democracy Project” at UCLA law school, told AFP.

“It has now become common among Trump’s supporters to believe that election theft in the US is common, despite all reliable evidence to the contrary. And these kinds of claims could well arise again in close elections.”

- Threat of violence -

The disputes could set the stage for a prolonged period of uncertainty, particularly as more than half the Republican midterm candidates are “election deniers” who have repeated Trump’s debunked claims of fraud in the 2020 polls.

“If candidates do not concede, or decide to litigate the election, this period will extend, with each day selecting some piece of election-day or counting-period evidence to amplify or extend,” the EIP report said.

Experts also warn that right-wing “election observers” –- mobilized by Trump supporters to hunt for voter fraud – could baselessly claim that they were unable to spot it after legal curbs on their activities, raising the possibility of violent confrontation.

The misinformation flooding social media has already included some calls for violence by election conspiracy theorists.

The SITE Intelligence Group, which monitors online extremists, said ultranationalists were encouraging an “armed, violent intervention” at Georgia ballot counting centers.

The call, reports said, came in response to news that the deadline for mail-in ballots in one state county had been extended after a logistical hiccup.

- ‘Stream of disinformation’ -

The Center for American Progress, a non-partisan think-tank, said misinformation tends to “not only continue but change and worsen in the post-election environment.”

“Election deniers may loudly launch baseless legal challenges. Politically motivated election officials may refuse to certify sound election results,” the think-tank said in a report.

“And most obviously, former President Trump may declare his intent to run for president in 2024, even before any newly elected officials are seated, giving him and his constant stream of disinformation increased media attention.”

Republican politicians, including Trump, began casting doubts on the integrity of the midterm election after technical problems with voting machines were reported in one part of Arizona.

“Can this possibly be true when a vast majority of Republicans waited for today to Vote?” Trump said on his Truth Social platform.

“Here we go again? The people will not stand for it!!!”

He was not alone.

“Hard to know if we’re seeing incompetence or something worse,” Blake Masters, a Trump-endorsed Senate candidate from Arizona, wrote on Twitter.

“All we know right now is that the Democrats are hoping you will get discouraged and go home.”

On Tuesday, officials in Arizona’s Maricopa County said about 20 percent of the 223 polling stations there were experiencing difficulties but it would not affect the accuracy of the vote.

“People have been spreading misinformation about our elections in the past few months,” the Maricopa County Recorder’s Office wrote on Twitter.

“In the weeks ahead (we anticipate) more of that. We’re prepared to combat misinformation with the truth.”