Thousands of protesters have gathered in key battleground states as the United States edged closer to an election result.

Protesters marched in Pennsylvania where President Donald Trump's party has filed a lawsuit based on allegations of voter fraud. There was no evidence to suggest any voter fraud had occurred.

Over 1,000 people have marched to the Pennsylvania Convention Centre where votes were currently being counted.

Sporadic protests have been taking place across the city throughout the day however groups have merged with a heavy police presence including police helicopters circling the crowd from above.

Crowds also marched in New York as the Democratic candidate Joe Biden moved closer to victory over President Trump.

In a brief statement Wednesday afternoon, Mr Biden said his campaign was on track to win 270 electoral votes but that he was not declaring victory until the count was completed in key states.

Dozens of supporters of Trump chanting “Stop the count!” descended on a ballot-tallying centre in Detroit, while thousands of anti-Trump protesters demanding a complete vote count in the still-undecided presidential contest took to the streets in cities across the US.

In New York City, thousands marched past boarded-up luxury stores on Manhattan’s Fifth Avenue, calling for every vote to be tallied. The march was largely peaceful, though police said they made at least 20 arrests after a smaller, rowdier group began protesting police misconduct by blocking traffic and setting fires.

In Chicago, protesters demanding a complete count marched through downtown and along a street across the river from Trump Tower.

Similar protests — sometimes about the election, sometimes about racial inequality — took place in at least a half-dozen cities, including Los Angeles, Seattle, Houston, Pittsburgh, Minneapolis and San Diego.

In Portland, Oregon, which has been a scene of regular protests for months, Gov. Kate Brown activated the National Guard after demonstrators engaged in what authorities said was widespread violence downtown, including smashing windows. Protesters in Portland were demonstrating about a range of issues, including police brutality and the counting of the vote.

Richard March came to an anti-Trump demonstration in Portland despite a heart condition that makes him vulnerable to COVID-19. “To cast doubt on this election has terrible consequences for our democracy,” he said. “I think we are a very polarized society now — and I’m worried about what’s going to come in the next days and weeks and months.”

The crowd in Detroit, angry over projections from the Associated Press and Fox News that have declared former Vice-President Joe Biden the winner of the state, chanted, “Count the votes” and “Fox News sucks.”

Hundreds of state police and left-wing protesters were locked in a tense standoff in downtown Portland late Wednesday 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 just before 8:30 pm ( 0430 GMT). 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.

Protesters who had gathered by Portland's river vowed to "protect the results" of Tuesday's close-run election and held banners proclaiming "Count Every Vote" and "The Vote is Over. The Fight Goes On."

"We want Trump out of office, that's the main focus," one protest leader told the crowd, to loud cheers.

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."