Joe Biden's top aide said the incoming US president would sign about a dozen executive orders on his first day in office, as police fearing violence from Donald Trump supporters staged a nationwide security operation ahead of the inauguration.

Authorities in Washington, where Wednesday's inauguration will take place, said they arrested a man with a loaded handgun and more than 500 rounds of ammunition at a security checkpoint.

The arrest underscores the tension in the US capital, which is resembling a war zone.

However, the man's family told US media he was a security guard, rejecting the idea he was intent on causing harm.

Incoming Biden chief of staff Ron Klain said in a memo to new White House senior staff that the executive orders would address the pandemic, the ailing US economy, climate change and racial injustice in America.

"All of these crises demand urgent action," Mr Klain said in the memo.

"In his first ten days in office, President-elect Biden will take decisive action to address these four crises, prevent other urgent and irreversible harms, and restore America's place in the world," he added.

As he inherits the White House from Mr Trump, Mr Biden, who attended Mass yesterday at St Joseph on the Brandywine Catholic church in Wilmington, Delaware, finds his plate overflowing with acute challenges.

The US is fast approaching 400,000 deaths from the Covid-19 crisis and logging well over a million new cases a week as the coronavirus spreads out of control.

The economy is ailing, with ten million fewer jobs available compared to the start of the pandemic.

Mr Biden this week announced plans to seek $1.9 trillion to revive the economy through new stimulus payments and other aid, and plans a blitz to accelerate America's stumbling Covid vaccine roll out effort.

On Inauguration Day Mr Biden, as previously promised, will sign orders including ones for the US to rejoin the Paris climate accord and reverse Mr Trump's ban on entry of people from certain Muslim majority countries, Mr Klain said.

"President-elect Biden will take action - not just to reverse the gravest damages of the Trump administration - but also to start moving our country forward," Mr Klain said.

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Meanwhile, Washington was under a state of high alert after a mob of President Donald Trump's supporters stormed the Capitol on 6 January. 

The assault left five people dead, including a police officer.

Security officials have warned that armed pro-Trump extremists, possibly carrying explosives, pose a threat to Washington as well as state capitals over the coming week.

Thousands of National Guard troops have been deployed in Washington and streets have been blocked off downtown with concrete barriers.

On Friday night, police arrested a Virginia man at a security checkpoint where he tried to use an "unauthorised" credential to access the restricted area where Mr Biden will be inaugurated.

As officers checked the credential against the authorised access list, one noticed decals on the back of Wesley Beeler's pick-up truck that said "Assault Life," with an image of a rifle.

Another had the message: "If they come for your guns, give 'em your bullets first," according to a document filed in Washington, DC Superior Court.

Under questioning, Mr Beeler told officers he had a Glock handgun in the vehicle.

A search uncovered a loaded handgun, more than 500 rounds of ammunition, shotgun shells and a magazine for the gun, the court document said.

Mr Beeler was arrested on charges including possession of an unregistered firearm and unlawful possession of ammunition.

But his father Paul told The New York Times his son had been working as a security guard on the Capitol grounds.

Asked if his son supported a peaceful transition of power, Paul Beeler told the newspaper, "That's the reason he's there."

In addition to the heavy security presence in Washington, law enforcement was out in force in state capitals around the US to ward off potential political violence.

Mass protests that had been planned for the weekend did not materialise yesterday, with security far outnumbering Trump supporters at several fortified statehouses, US media reported.

In St Paul, Minnesota, for example, hundreds of law enforcement officers, some armed with long guns, ringed the Capitol with National Guard troops providing backup. 

The number of protesters totalled about 50.