Isolated problems with voting machines and absentee ballots on Tuesday left officials scrambling to reassure voters of the integrity of the US election, after two years of unfounded claims of fraud dented confidence in democracy.

Issues were reported with ballots not being received in Georgia, where a knife-edge Senate battle is being played out, and long queues were seen in Texas after some machines there broke down.

Meanwhile, a fifth of voting machines in one part of Arizona were not working, in a county that became ground zero for the election denialism driven by Donald Trump after his defeat in 2020.

Officials in Maricopa County, which includes the city of Phoenix, the fifth most populous US city, said a minority of the 223 polling stations were experiencing difficulties.

"We've got about 20 percent of the locations out there where there's an issue with the tabulator," said Maricopa County Board of Supervisors Chairman Bill Gates.

Gates said the broken-down machines would not affect the probity of the poll.

"We also have a redundancy in place," Gates added, saying paper ballots would be transferred in a secure box to a central election facility for tabulation.

President Joe Biden won Arizona by a razor-thin 10,000 votes in 2020, with cosmopolitan and densely populated Maricopa County key to his support.

But elsewhere in the state, which has in the past leaned Republican, the victory was viewed with suspicion and sparked conspiracy theories about a fix.

Donald Trump and his supporters have spent much of the last two years pushing groundless claims of ballot stuffing, despite numerous investigations -- including a Republican-funded one -- that found no evidence of fraud.

Republican candidates for secretary of state, governor and a US Senate seat from the state all subscribe to the debunked theory, and say they would not have certified Biden's win.

Masked poll watchers, some of them armed, have hung around early voting drop boxes, in what they said was an effort to prevent ballot stuffing, until a judge ordered them to keep their distance.

Nonpartisan county officials have mounted a huge voter confidence operation, holding regular open meetings and inviting citizens to come and inspect their voting security procedures.

But Tuesday's breakdowns were taken as evidence for some Republicans that there was cheating afoot.

Trump took to his Truth Social platform to denounce the county.

"Reports are coming in from Arizona that the Voting Machines are not properly working in predominantly Republican/Conservative areas," he wrote.

"Can this possibly be true when a vast majority of Republicans waited for today to Vote? Here we go again? The people will not stand for it!!!"
Voters in line in Maricopa agreed.

"It's happening all over again," said one voter, who did not wish to give his name.

Donald Newton, 82, said it was not acceptable.

"This machine should have been tested and working a long time ago, you know, last week," he said.

- Texas, Georgia -

In Georgia, where Trump-endorsed former NFL star Herschel Walker is battling incumbent Raphael Warnock, officials in Cobb county shipped hundreds of forms to voters overnight after a clerical error affecting people who requested absentee ballots.

More than 1,000 people were affected, some of whom have since decided to vote by another method. The rest will have their votes counted as long as they are postmarked by election day, county officials said.

In Harris County, the third most populous county in Texas, voters were finding closed gates, long lines and non-operational voting machines, the Washington Post reported.

County elections office spokesperson Nadia Hakim said there had been complaints from more than half a dozen polling stations, including a busy spot where a third of the 60 voting machines were not working, creating long lines for people waiting to cast their ballot.

"That is our busiest polling location, so if anything goes down over there, it is super noticeable," the paper quoted her as saying, noting the machines were fixed by midmorning.

Nonpartisan voter registration organization Vote.org said the isolated incidents were not expected to alter the ballot.

"There are reports in several states that some voting machines are having technical problems," CEO Andrea Hailey said.

"This can happen, and election workers and state officials are working hard to resolve those issues and ensure voters have other options to cast their ballots today.

"This type of transparency from election officials shows the strength and resiliency of our democracy and the people and systems that uphold it."