More than 300 supporters of President Donald Trump have gathered outside an election office in Arizona chanting "count the vote" as the US braces for a fresh wave of protests as an election result nears.
Maricopa County in Arizona is a key area where around 300,000 votes are still to be counted out of a total of 350,000 across the state.
Arizona has been called for Democrat Joe Biden by Fox News and the Associated Press, but remains contested according to other news outlets. Both Biden and Trump are confident of a win in the state.
On Wednesday evening local time, Trump supporters, some of them armed, gathered with megaphones, claiming the vote had been stolen from Trump.
Counting officials worked under police protection after some protesters attempted to push inside the centre.
Some election workers and members of the media were escorted to their vehicles for their safety, officials said.
Early results show Biden holding a wafer-thin lead in the state. Arizona Secretary of State Katie Hobbs told ABC News she doesn't expect a recount as the "our recount margins are very narrow".
A recount in Arizona is automatically triggered if the margin is within 0.1 per cent of total number of votes.
"We have said from the beginning that this takes time, and we're going to focus on making sure every valid vote counts," she said.
"It's not looking like today, probably closer to tomorrow that we'll be closer to getting through all those ballots."
Protesters wearing Trump attire filled a car park at the election centre.
Republican US representative Paul Gosar joined the crowd and said: "We're not going to let this election be stolen. Period."
President Trump has stoked the tensions, writing "STOP THE COUNT!" on Twitter.
Other tweets from Trump alleging election fraud were censored by Twitter, with the warning "Some or all of the content shared in this tweet is disputed and might be misleading about an election or other civic process".
Observers from both parties are allowed to view the processing of ballots inside the Arizona election centre and the procedure is being livestreamed at all times.
It comes as protests have broken out in several parts of the US amid a tense wait for an election result, with clashes in Portland, New York and Detroit.
In Portland, hundreds of state police and left-wing protesters were locked in a tense standoff after rampaging anti-Trump groups smashed shop windows a day after the election, prompting the state governor to activate the National Guard.
The Multnomah County Sheriff's office declared a riot and made at least nine arrests, citing "widespread violence" in the city's downtown area and repeatedly warning it could deploy munitions and tear gas.
Armed police advanced on demonstrators in unison but there were no clashes, according to an AFP reporter at the scene.
The protesters had earlier attended a peaceful rally in a downtown park hosted by a coalition of far-left, anti-capitalist groups featuring lectures and music.
"The mass gathering in downtown Portland is still declared a riot. Leave the area now," the sheriff's office posted on Twitter. It earlier said officers were being targeted with projectiles, such as glass bottles.
"In the interest of public safety, Governor Kate Brown, under advice of the Unified Command, has activated the use of the Oregon National Guard to assist local law enforcement," it said.
Portland has been the scene of months of clashes between police and protesters, angered at the repeated killings of Black Americans by law enforcement officers across the country.
But several of the demonstrators were openly carrying firearms, including rifles, and one anti-racism and anti-imperialism banner showed an image of an assault rifle, with the slogan "We Don't Want Biden. We Want Revenge".
Meanwhile, destructive protests have erupted in New York as the count of votes continues.
The New York Post reported police clashed with protesters as some set fires in the streets and allegedly spat at officers.
The National Guard has also been deployed in Philadelphia, Pennsylvania, and protests have been seen in Minnesota and outside the White House in recent days.
In Detroit, Trump supporters also descended on voting centres calling for the count to be stopped. Elsewhere, Trump voters wanted it to continue, sparking widespread confusion.
Trump has repeatedly said that mail-in ballots should not be counted and stoked fears of voter fraud despite a lack of evidence.
Officials have assured voters every ballot will be counted.
- With wires