Pro-Trump protesters — some of them openly carrying rifles and handguns — rallied outside vote-tabulation centres in a few cities around the country Friday, responding to groundless accusations from President Donald Trump that the Democrats were trying to steal the White House.

Elections officials in several states where Democrat Joe Biden was ahead said the anger outside their doors made them fear for the safety of their employees.

Roughly 100 Trump supporters gathered for a third straight day in front of the elections centre in Phoenix, where hundreds of workers were processing and counting ballots.

“Arrest the poll workers!" the crowd chanted, demanding four more years in office for Trump. Sheriff's deputies kept protesters in a “free speech” zone away from the entrance to the building.

“When we start auditing some of these voter rolls, their fraud may actually be exposed,” conservative activist Charlie Kirk told the crowd, eliciting cheers.

In Detroit, dozens of Trump supporters returned to the streets outside the city's convention centre, where election workers counted ballots.

“Stop the steal!” the protesters chanted. Some carried signs that read, “Make Elections Fair Again” and “We Love Trump". Police cordoned off streets leading to the building and maintained a close watch on the protest.

The county treasurer in Detroit, Eric Sabree, said he had closed his office because of threats. In a statement, Sabree said the decision was made “in the interest of the safety of taxpayers and our staff” and because of “credible information” from the sheriff's office.

In Philadelphia, two men with handguns were arrested Thursday night near the convention centre where the vote-counting that could decide the White House race was going on.

The men, ages 42 and 61, had driven up in a Hummer from Virginia and did not have permits to carry the weapons in Pennsylvania, police said. A military-style rifle and ammunition were found inside their vehicle, Police Commissioner Danielle Outlaw said. The car had a window sticker for the right-wing conspiracy theory QAnon.

District Attorney Larry Krasner did not say why the men had come to Philadelphia but said there were no indications they were part of an extremist group.

In Rhode Island, about 100 protesters rallied outside the state board of elections headquarters, demanding a recount in an overwhelmingly Democratic state where Biden won with more than 59 per cent of the vote.

Protesters said ballots were illegally dumped in Rhode Island, but offered no evidence. State elections officials have said they have no evidence of fraud.

“We demand a recount in Jesus' name!” protest leader Kathleen Forant shouted, as state police stood nearby.