US President Donald Trump officially set a lofty goal of doubling economic growth to 4 per cent through tax reform, looser regulation, building infrastructure and overhauling trade deals, hours after paradoxically championing protectionism in a stridently nationalist inauguration speech.
Mr Trump, sworn in as the 45th US President in Washington, swiftly signed executive orders to begin unwinding former president Barack Obama's healthcare insurance law, halt new regulations and suspend a government subsidy for mortgage insurance. Reflecting the 45th President's pro-fossil fuels energy policy, climate change references were quickly deleted from the White House website. He also committed to withdrawing from the Trans-Pacific Partnership, the trade deal with includes Australia.
Depicting an America in "carnage" in a blistering inaugural address, the billionaire businessman rebuked Republican and Democratic lawmakers and past presidents gathered behind him at the US Capitol for failing to deliver prosperity to ordinary Americans.
Mr Trump, surrounded by his family and new Vice-President Mike Pence, warned the world that his domestic and international policies, including trade and defence, would be embedded with "America First" principles.
"Every decision on trade, on taxes, on immigration, on foreign affairs, will be made to benefit American workers and American families," Mr Trump said under light rain on the steps of the US Capitol Building.
"We must protect our borders from the ravages of other countries making our products, stealing our companies, and destroying our jobs.
"Protection will lead to great prosperity and strength."
The White House at the weekend laid out a high-level agenda to create 25 million American jobs over a decade.
If the largest economy doubles annual economic growth on a sustained basis from about 2 per cent achieved during the Obama era, it could be a boon for the rest of the world.
However, economists believe hitting such an audacious target will be a massive challenge due to an ageing population, soft productivity, a middling global economy and Mr Trump's scepticism of international trade agreements and large-scale immigration.
The Republican President's official trade policy released at the weekend pledged to withdraw from the Trans-Pacific Partnership, renegotiate a regional trade pact with Mexico and Canada, and – in a tacit targeting of China – "crack down" on nations that violate trade rules.
Investors weighed his inauguration promise of building new roads, bridges, airports, tunnels and railways "with American hands and American labour" and his earlier touted plan to slash and reform taxes, against concerns about trade protectionism creeping in.
AMP Capital head of investment strategy Shane Oliver said it was more likely Mr Trump would be a pragmatist rather than a populist on trade to ensure he didn't threaten jobs, but he noted there was a high risk of a "tit for tat trade war" between the US and China.
"Markets are now waiting for more evidence that Donald Trump will deliver on fiscal stimulus and deregulation but uncertainty remains high about what he will do on trade," Dr Oliver said.
The US dollar edged lower against most currencies during Mr Trump's inaugural address.
Shares on Wall Street temporarily dipped from earlier highs, before recovering with the S&P; 500 finishing up 0.34 per cent on Friday.
On foreign policy objectives that may have implications for close partners including Australia, the Trump administration will make defeating "radical Islamic terror groups" its top goal.
Mr Trump 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."
Mr Obama refused to use the term "Islamic" terrorism, arguing it was divisive and unfairly tarnished the vast majority of peaceful Muslims.
Some foreign policy experts expressed alarm about signs Mr Trump may retreat from US global leadership under his "America First" banner, and open the way for recalcitrant states such as Russia to be more aggressive.
"America First, the pursuit of narrow self-interest, risks prompting others to do same, reducing US influence and world stability/prosperity," Council on Foreign Relations president Richard Haass said in a social media post.
In words that will reassure foreign allies, new Defence Secretary James Mattis, one of the first two Trump cabinet members sworn in, said the US would seek to strengthen alliances.
Mr Trump flagged upcoming meetings with the leaders of Canada, Mexico and the United Kingdom.
The fiery inaugural speech, in the presence of hundreds of thousands of elated supporters and scores of protesters around the US Capitol Building, echoed his populist election campaign pitch.
The new President's doubling down on his pre-election nativism and economic populism is a sharp turn from the traditional Republican philosophy of open trade and international engagement.
It sets up a potential clash with party colleagues in Congress.
Since the November 8 election, sharemarkets in advanced economies including the US and Australia have rallied on bullish bets on Mr Trump's promises of slashing taxes for business and individuals, unwinding regulation and boosting infrastructure investment.
The Dow Jones Industrial Average is up 8 per cent and S&P; 500 6 per cent higher since the election.
Mr Trump and first lady Melania attended three presidential balls on Friday night, dancing and mingling with guests, before the President began his first full day as Commander-in-Chief on Saturday.
He attended a national prayer service and visited the Central Intelligence Agency, one of the spy organisations he last week likened to "Nazi" Germany for suspicion they leaked damaging information about him.
Mr Trump, whose CIA nominee Mike Pompeo has been delayed by Senate Democrats from commencing in the job, assured staff he believed the agency has "really special amazing people" and that "I am so behind you".
The former celebrity TV star blamed the "dishonest media" for inventing a "feud" with the CIA and also complained the press had underestimated the size of his inauguration crowd.
He alleged the media had said he only had 250,000 people at the inauguration, when "it looked like a million, million and a half people".
Mr Trump's spokesman Sean Spicer claimed he had drawn "the largest inaugural crowd ever" though early estimates suggested it was far short of the 1.8 million attributed to Mr Obama in 2009.
On Saturday hundreds of thousands of people marched for women's rights and against Mr Trump in the US capital, while a total of millions rallied in other US and cities around the world.
Homeland Security Secretary John Kelly, responsible for Mr Trump's hardline immigration policy that will begin with expelling foreign criminals and building a wall on the Mexico border, was confirmed by the Senate and sworn in.
Just hours after his inauguration, Mr Trump quickly signed executive actions to freeze any new regulations and slash government red tape that business complained had swelled during Mr Obama's eight years in power.
Mr Trump requested waivers for states, people and businesses from any provisions in the Obamacare health insurance laws that impose a cost or burden such as tax penalty.
