Donald Trump will be sworn in on Friday as the 45th president of the United States, taking power over a divided country after a savage campaign and setting the country on a new, uncertain path at home and abroad.

In a ceremony likely to draw 900,000 people, including protesters, Trump and his vice president, Mike Pence, will take the oath of office at midday (1700 GMT) outside the domed U.S. Capitol, with U.S. Chief Justice John Roberts presiding.

"It all begins today!" Trump wrote in a note on Twitter at about 7:30 a.m. "I will see you at 11:00 A.M. for the swearing-in. THE MOVEMENT CONTINUES - THE WORK BEGINS!"

Security was tight around the White House and Capitol. Streets near the president's home were blocked to traffic by empty buses and dump trucks or temporary pedestrian security checkpoints where law enforcement officers and National Guard troops checked people's bags.

Checkpoints around the National Mall in front of the Capitol opened early to begin admitting guests, some of them wearing red caps bearing Trump's "Make America Great Again" slogan. They were barred from bringing selfie sticks, coolers for beverages, and long umbrellas despite the rainy weather.

Most of the area was orderly, but about 100 protesters shouted slogans near one checkpoint and linked arms to block people from entering. Police in riot gear pushed them back into an intersection to allow people attending the inauguration to reach the checkpoints.

Trump, 70, enters the White House with work to do to bolster his image. During a testy transition period since his stunning November election win, the wealthy New York businessman and former reality TV star has repeatedly engaged in Twitter attacks against his critics, so much so that one fellow Republican, Senator John McCain, told CNN that Trump seemed to want to "engage with every windmill that he can find."

An ABC News/Washington Post poll this week found only 40 percent of Americans viewed Trump favourably, the lowest rating for an incoming president since Democrat Jimmy Carter in 1977, and the same percentage approved of how he has handled the transition. (http://abcn.ws/2jU9w63)

His ascension to the White House, while welcomed by Republicans tired of Democrat Barack Obama's eight years, raises a host of questions for the United States.

Trump campaigned on a pledge to take the country on a more isolationist, protectionist path and has vowed to impose a 35 percent tariff on goods on imports from U.S. companies that went abroad.

His desire for warmer ties with Russian President Vladimir Putin and threats to cut funding for North Atlantic Treaty Organization nations has allies from Britain to the Baltics worried that the traditional U.S. security umbrella will be diminished.

In the Middle East, Trump has said he wants to move the U.S. embassy in Israel from Tel Aviv to Jerusalem, at the risk of angering Arabs. He has yet to sketch out how he plans to carry out a campaign pledge to "knock the hell out of" Islamic State militants.

DEMOCRATS' BOYCOTT

The inaugural festivities may have a more partisan edge than usual, given Trump's scorching campaign and continuing confrontations between him and Democrats over his take-no-prisoners Twitter attacks and pledge to roll back many of Obama's policies.

More than 50 Democratic lawmakers plan to stay away from the proceedings to protest Trump, spurred on after he derided U.S. Representative John Lewis of Georgia, a hero of the civil rights movement, for calling him an illegitimate president.

Thousands of anti-Trump protesters were expected among an inauguration crowd that organizers estimated will be upwards of 900,000. Many demonstrators will participate in the "Women's March on Washington" on Saturday. Protests are also planned in other cities in the United States and abroad.

Trump, whose Nov. 8 victory stunned the world, will start his presidency with a 20-minute inaugural address that he has been writing himself with the help of top aides. It will be "a very personal and sincere statement about his vision for the country," said his spokesman, Sean Spicer.

"He'll talk about infrastructure and education, our manufacturing base," Spicer told reporters. "I think it's going to be less of an agenda and more of a philosophical document, a vision of where he sees the country, the proper role of government, the role of citizens."

Keith Kidwell, chairman of the Republican Party in Beaufort County, North Carolina, was among the crowds on Friday, eager to see the start of the Trump presidency.

"I cling to my guns and my Bible. I've been waiting a long eight years for this day," said Kidwell, adding he initially supported U.S. Senator Ted Cruz to be the Republican presidential nominee but was now squarely behind Trump.

QUICK ACTION

Trump's to-do list has given Republicans hope that, since they also control the U.S. Congress, they can quickly repeal and replace Obama's signature healthcare law, approve sweeping tax reform and roll back many federal regulations they say are stifling the U.S. economy.

Democrats, in search of firm political footing after the unexpected defeat of their presidential candidate, Hillary Clinton, are planning to fight him at every turn. They deeply oppose Trump's anti-immigrant rhetoric from the campaign trail and plans to build a wall along the southern U.S. border with Mexico.

Trump's critics have been emboldened to attack his legitimacy because his win came in the Electoral College, which gives smaller states more clout in the outcome. He lost the popular vote to Clinton by about 2.9 million.

"Any time you don’t win the popular vote but you win by the Electoral College it makes people come unglued," said presidential historian Douglas Brinkley. "It angers people that somebody can win the popular vote but you're not president."

Trump's critics also point to the conclusion of U.S. intelligence agencies that Russia used hacking and other methods during the campaign to try to tilt the election in the Republican's favour. The president-elect has acknowledged the finding - denied by Moscow - that Russia was behind the hacking but said it did not affect the outcome of the election.

To his supporters, many of them working-class whites, Trump is a refreshingly anti-establishment figure who eschews political correctness. To critics - including Obama who during the campaign called Trump temperamentally unfit for the White House - his talk can be jarring, especially when expressed in tweets.

But while a Wall Street Journal opinion poll showed a majority of Americans would like Trump to give up on Twitter, Trump said he would continue tweeting because the U.S. news media does not treat him fairly.