Donald Trump sworn in as 45th US president

Donald Trump is sworn in as 45th President of the United States on Jan 20, 2017 at the US Capitol in Washington, DC. (Mark RALSTON / AFP)

Hundreds of thousands of people stood in the rain-splattered National Mall to see the 70-year-old Republican billionaire take the oath of office and deliver a stridently populist and at times angry call-to-arms.

"From this day forward, a new vision will govern our land," Trump said, promising an end to business-as-usual in Washington. "From this moment on, it's going to be only America First."

"Today we are not merely transferring power from one administration to another or from one party to another, but we are transferring power from Washington, DC. And giving it back to you, the people."

"Together we will make America strong again. We will make America wealthy again. We will make America proud again. We will make America safe again. And, yes, together, we will make America great again," Trump said.

President Donald Trump delivers his inaugural address at the West Front of the US Capitol in Washington, DC. (Alex Wong/Getty Images/AFP)

Just moments before, the 70-year-old Republican billionaire placed his left hand on a bible used by Abraham Lincoln and recited the 35-word oath spoken since George Washington.

Trump's inauguration caps the improbable rise to power of the Manhattan real estate mogul, who had never before held elected office, served in the government or the armed forces.

This was far from the typical optimistic inaugural address that tries to brook political divides and lift Americans' gaze up to the horizon.

Trump painted parts of America as a dystopian hell, with mothers trapped in poverty and "rusted-out factories scattered like tombstones across the landscape."

"This American carnage stops right here and stops right now," he said.

It was a deliberate and striking contrast from the uplifting message of outgoing president Barack Obama, who was among the dignitaries in attendance.

Obama and his wife Michelle departed the Capitol by helicopter moments after the swearing-in ceremony, turning a page on eight years of Democratic leadership in the White House.

US President Barack Obama (R) greets President-elect Donald Trump as he arrives at the US Capitol in Washington, DC, before his swearing-in ceremony. (Mandel NGAN/AFP)

At a Congressional luncheon afterward, Trump led a standing ovation for his defeated rival Hillary Clinton, saying he was "honored" that she and former president Bill Clinton attended his inauguration.

SPORADIC VIOLENCE

When Trump descended the escalators of his glitzy New York tower in June 2015, his run for office was dismissed and even mocked.

His supporters, many shunned by friends for supporting a man who has been labeled a racist and bigot by his critics, will now become power players in the White House and footsoldiers a monumental battle of ideas.

His message to them was one of vindication: "The forgotten men and women of our country will be forgotten no longer. Everyone is listening to you now."

In the primaries, Trump dominated a crowded Republican presidential field with smash-mouth rhetoric and star power. He rode that same wave of anti-elite sentiment to victory over Clinton in the November election.

For Trump's critics, there was disbelief that a man who 19 months ago hosted "The Apprentice" is now leader of the free world.

A short distance from the route of Trump's inaugural parade, there were demonstrations throughout the morning - marred by isolated outbreaks of violence on their fringe.

After Trump spoke, 400 to 500 protesters smashed storefronts and hurled missiles at riot police, who responded with tear gas. More than 90 people were arrested.

Demonstrators hold signs before the inauguration of President-elect Donald Trump in Washington, DC. (ZACH GIBSON/AFP)

Most of the demonstrations in the city were peaceful however - whether people came to register anger, dissent or dismay at Trump's election. A bigger anti-Trump rally is planned for Saturday.

Public interest lawyer Renee Steinhagen, 61, came down from New York to join the protests.

"I'm doing this to express resistance to the change that await us," she said. "This administration seems more extreme than any other. This is a simple act of resistance. It's better than staying at home."

He arrives to the White House with a 37 per cent approval rating, the lowest on record, according to a CBS News poll.

'RADICAL ISLAMIC TERRORISM'

Trump quickly got to work, signing a waiver for former general James Mattis to become the civilian head of the Department of Defence.

He also signed a proclamation for a "national day of patriotism."

For the next few weeks his team plans a series of daily executive orders to roll back Obama's agenda.

Trump has also vowed to re-examine long-running alliances with Europe and in Asia.

"For many decades we've enriched foreign industry at the expense of American industry, subsidised the armies of other countries while allowing for the very sad depletion of our military," he said.

"We will reinforce old alliances and form new ones and unite the civilised world against radical Islamic terrorism, which we will eradicate completely from the face of the Earth."

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