Hours before Trump gets hands on US nuclear codes

Controversial business tycoon Donald Trump will be sworn in as the 45th president of the United States on Friday - capping his improbable journey to the White House and beginning a four-year term that promises to shake up Washington and send reverberations across much of the globe.

The president-elect is expected to place his hand on Abraham Lincoln's bible, recite the oath of office on the steps of the Capitol and become the most powerful man on earth -- complete with a nuclear arsenal at his erratic fingertips -- before a gathering of an estimated 800,000 on the National Mall in the centre of the nation's capital.

The 70-year-old, who began his unpredictable political career just 19-months-ago, will be the oldest president to serve in the Oval office, as well as the first to never have served in the government or the armed forces.

In brief remarks on the eve of becoming president, Trump vowed to bring unity, but there was also a rallying cry for his base.

"We're going to unify our country," he said, before telling supporters: "You're not forgotten anymore."

"We're going to get our jobs back. We're not going to let other countries take our jobs any longer. We're going to build up our great military."

After his speech, Trump will attend a luncheon inside the Capitol, before heading back to the White House to begin the business of governing.

Despite this, the provocative figure will enter office with a mere 37 percent approval rating, the lowest on record, according to a CBS News poll.

For his critics, Trump's arrival in Washington on-board an Air Force jet on Thursday was deemed a hostile takeover rather than a traditional changing of the guard.

Protests erupted across the city centre in the lead up to the much-anticipated inauguration, with demonstrators declaring Trump illegitimate.

On Thursday evening hundreds of anti-Trump protesters demonstrated outside a Washington pro-Trump event, before police used chemical spray to disperse the crowd.

The scenes were repeated just hours before the official inauguration ceremony on Friday and are expected to escalate during a mass rally planned for Saturday. 

As Obama's White House staff cleaned out their desks and the normally busy corridors of the West Wing fell quiet, many staffers expressed relief at the prospect of rest, but foreboding about the road ahead.

That sentiment is echoed across much of the world, including the Middle East where longstanding-US allies await an unpredictable Trump administration.