Outgoing President Donald Trump entered the White House four years ago as a brash billionaire outsider, but he is being ousted by a polar opposite whose devotion to service, deep knowledge of Washington, and personal scars will unquestionably set a different tone.

Biden, a 78-year-old former vice president and longtime senator, will take the oath of office at noon (1700 GMT) on the US Capitol's West front, the very spot where pro-Trump rioters clashed with police two weeks ago before storming Congress in a deadly insurrection.

While a transition of power will occur much as it has for more than two centuries, this inauguration is unlike any other.

Official Washington has taken on the dystopian look of an armed camp, protected by some 25,000 National Guard troops tasked with preventing any repeat of this month's attack.

Members of the US National Guard walk outside the US Capitol on January 19, 2021 in Washington, DC, ahead of the 59th inaugural ceremony for President-elect Joe Biden and Vice President-elect Kamala Harris. (Agence France Presse/Brendan Smialowski)

And with the pandemic raging, the general public is essentially barred from attending the swearing-in, leading to unprecedented optics: an empty National Mall on Inauguration Day.

With the death toll soaring past 400,000, Biden on Tuesday led a powerful tribute to victims of Covid-19 as he arrived in Washington.

Biden, who has suffered deep personal tragedy and is known for his public displays of emotion, has stressed the need to unite the country after Trump's chaos.

"It's hard sometimes to remember, but that's how we heal. It's important to do that as a nation," Biden said in somber remarks at the reflecting pool in front of the Lincoln Memorial.

Trump snub

Inauguration eve is normally a time of massive crowds gathering in the capital, but Biden, joined by Vice President-elect Kamala Harris, was almost alone at the reflecting pool.

On the Mall's grassy expanse, some 200,000 flags have been planted to represent the absent crowds at the inauguration.

US President-elect Joe Biden, his wife Jill Biden, Vice President-elect Kamala Harris and her husband Doug Emhoff attend a coronavirus disease (COVID-19) memorial event at the Lincoln Memorial in Washington, US. January 19, 2021. (Reuters/Tom Brenner)

Trump, who has not appeared in public for a week, broke days of silence with a pre-recorded farewell video address on Tuesday.

For the first time, he asked Americans to "pray" for the success of the incoming administration -- a change from months spent persuading his Republican followers that the Democrats cheated their way to election victory.

Trump, whose efforts to combat the Covid-19 pandemic and console its victims have been widely criticized, will snub Biden by not attending the inauguration.

He has also yet to personally congratulate Biden, who first ran for president in 1987, on his win, and did not invite him for the customary cup of tea in the Oval Office.

In one of his last acts before he flies to Florida on Wednesday morning, Trump issued scores of pardons to people convicted of crimes or facing charges, including key allies.

Influential former Trump aide Steve Bannon -- charged with defrauding people over funds raised to build the Mexico border wall, a flagship Trump policy -- was among 73 people on a list of pardons released by the White House early Wednesday.

Neither Trump nor his relatives were on the list.

Former Trump fund-raiser Elliott Broidy was similarly pardoned, after pleading guilty last year to conspiring to violate foreign lobbying laws.

The rapper Lil Wayne, who last month pleaded guilty to possession of a firearm and ammunition by a convicted felon, and faced 10 years in jail, also made the list.

Tensions have soared on Capitol Hill, where the Senate is expected to put Trump on trial soon, following his record second impeachment by the House of Representatives over the Capitol riot.

The spectacle will clash with the opening days of Biden's tenure, as the new president seeks to swiftly confirm his Cabinet picks and push through aggressive legislation including a $1.9 trillion rescue package.

'I'll get right to work'

"We don't have a second to waste when it comes to tackling the crises we face as a nation," Biden tweeted late Tuesday.

"That's why after being sworn in tomorrow, I'll get right to work."

His inaugural speech will last between 20 and 30 minutes, according to a source familiar with preparations, and "he will reach out to all Americans, and call on every citizen to be part of meeting the extraordinary challenges facing all of us."

To symbolize the new spirit, Biden has invited the two top senators -- Democrat Chuck Schumer and Republican Mitch McConnell -- and other congressional leaders to attend a church service with him Wednesday before the inauguration.

Biden's first day is expected to be packed, with aides saying recently he would sign perhaps a dozen executive orders that could address the pandemic, the ailing US economy, climate change and racial injustice in America.