Dozens of supporters of President Donald Trump chanting “Stop the count!” descended on a vote-tallying centre in Detroit on Wednesday, as Americans on both political sides vented their anger and frustration over the undecided presidential contest at protests around the country.

The Detroit protests started soon before The Associated Press declared Democratic candidate Joe Biden had won Michigan.

Video shot by local media showed angry people gathered outside the TCF Centre and inside the lobby, with police officers lined up to keep them from entering the counting area. They chanted “Stop the count!” and “Stop the vote!”

Election 2020 Protests Detroit
A Democrat supporter holds a sign outside the TCF Centre in Detroit on Wednesday (David Goldman/AP)

In New York City, by contrast, 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 made at least 20 arrests after a smaller, rowdier group began protesting police misconduct.

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.

Michigan has been on edge for months over fears of political violence. Anti-government protesters openly carried guns into the state Capitol during protests over coronavirus restrictions in the spring, and six men were arrested last month on charges of plotting to kidnap Democratic governor Gretchen Whitmer

Election 2020 America Reacts
Election challengers are forced to wait outside after an election official, right, closed the door to the central counting board (Carlos Osorio/AP)

Earlier, the Republican campaign filed suit in a bid to stop the count, demanding Michigan’s Democratic secretary of state allow in more inspectors.

Mr Trump has repeatedly insisted without evidence that there are major problems with the voting and the counting.

Michigan Attorney General Dana Nessel, a Democrat, insisted both parties and the public had been given access to the tallying “using a robust system of checks and balances to ensure that all ballots are counted fairly and accurately”.

On Tuesday night, scattered protests broke after voting ended, stretching from Washington DC to Seattle, but there was no widespread unrest or significant violence.

In Portland, Oregon, Richard March came to an anti-Trump protest 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 polarised society now — and I’m worried about what’s going to come in the next days and weeks and months.”

The prolonged task of counting this year’s deluge of mail-in votes raised fears that the lack of clarity in the presidential race could spark conflict.

Other anti-Trump demonstration were set for Wednesday evening, with protesters gathering in cities including Houston and Minneapolis.