Trump will get wake-up call when he takes office, Obama says

In a news conference at the White House, Obama said the freewheeling Trump could not be as outspoken as he was during the long and bitter campaign that ended last week with the Republican's surprise win over Democrat Hillary Clinton.

Subdued and carefully choosing his words, Obama gave what appeared to be dispassionate advice to his successor free of much of the partisan rancour that marked the election campaign.

"This office has a way of waking you up," Obama said. "Those aspects of his positions or predispositions that don't match up with reality, he will find shaken up pretty quick because reality has a way of asserting itself."

The two men met in the Oval Office last week to begin the transition of power. Obama said on Monday he believed Trump would be pragmatic in office and not approach the country's problems from an ideological perspective.

"There are going to be certain elements of his temperament that will not serve him well, unless he recognises them and corrects them," Obama said.

"Because when you're a candidate and you say something that is inaccurate or controversial it has less impact than it does when you're president of the United States. Everybody around the world is paying attention. Markets move," he said.

Obama declined to wade into a controversy over Trump's appointment of right-wing firebrand Stephen Bannon as his chief strategist, saying it would "not be appropriate" for him to comment on Trump's appointments.

But Obama, who criticised Trump's temperament during the campaign, said it was important for Trump to send signals of unity after the hard-fought campaign. He said the political gifts that allowed the Republican to upset Clinton would be put to good use in the White House.

"I've been encouraged by his statements on election night about the need for unity, his interest in being president for all people," Obama said. "In an election like this that was so hotly contested and so divided, gestures matter."