One person has been shot at an anti-Trump demonstration in Portland, as tens of thousands of people took to the streets across the United States for a fourth straight day after Donald Trump’s surprise election victory.

A police statement said the suspected shooter had been in a vehicle on the Morrison Bridge when there was a confrontation with a protester.

“The suspect got out of the vehicle and fired multiple shots injuring the victim,” the statement said.

Police ordered evacuation of area following shooting. Photo: AAP

Police posted to Twitter: “One person down. Everyone needs to leave the area immediately”.

The victim was treated at the scene before being taken by ambulance to a Portland hospital with non-life-threatening injuries.

Police detained four people in connection with the shooting, but a motive was still unclear.

The four people detained are believed to be gang members, but the victim is not.

The shooting followed rowdy Friday night protests, when police used tear gas in response to “burning projectiles” thrown at officers, police said on Twitter. Authorities reported instances of vandalism and assault during a rally that organisers had billed as peaceful earlier in the day.

Protests took place in several US cities, including in Miami, Atlanta, Philadelphia, New York, San Francisco and Portland.

Meanwhile, US President-elect Donald Trump is taking on the massive undertaking of creating a new administration as a circus-like atmosphere unfolds around his building in Manhattan.

While he’s announced one decision – putting vice president-elect Mike Pence in charge of the transition instead of Chris Christie – Mr Trump must identify other people for top White House jobs and Cabinet posts.

He was apparently trying to sort through names as he holed himself up in Trump Tower and protesters swarmed outside behind barricades protecting the building and ritzy stores along Fifth Avenue.

At one point, documentary filmmaker Michael Moore, a liberal critic of Mr Trump who nevertheless had predicted his victory, entered the tower lobby with a camera crew in tow and asked to see Mr Trump.

“I just thought I’d see if I could get into Trump Tower and ride the famous escalator,” said Moore, who did just that until he reached the fourth floor and the Secret Service told him he could go no higher.

Protesters in Los Angeles are showing their antipathy for President-elect Trump. Photo: ABC

Moments later, Nigel Farage, the head of the “Leave” movement that won Britain’s vote to exit the European Union, also arrived and was allowed up.

More than 200 people, carrying signs, gathered on the steps of the Washington state Capitol. The group chanted “not my president” and “no Trump, no KKK, no fascist USA”.

In Tennessee, Vanderbilt University students sang civil rights songs and marched through campus across a Nashville street, temporarily blocking traffic.

https://twitter.com/dinovopj/status/797329514179149824

Anti-Trump rally scheduled for Inauguration Day

With the country evenly divided, many voters were shocked by the result given that opinion polls failed to predict Mr Trump’s triumph.

The Republican Party also managed to maintain its majorities in both houses of Congress in Tuesday’s vote.

More anti-Trump demonstrations were planned for the weekend, and a group calling itself #NotMyPresident has scheduled an anti-Trump rally for Washington on January 20, when Mr Trump formally succeeds President Barack Obama.

Republican National Committee Chairman Reince Priebus acknowledged on Friday the tight race with Mrs Clinton, but said anti-Trump protesters had to accept the election results.

He pointed to Mr Trump’s call for unity and meetings on Thursday with Mr Obama and Republican leaders as reasons for reassurance.

Mr Trump’s base of support in the election was the broad middle of the country, with voters in states that had long supported Democrats shifting to him after he promised to renegotiate trade deals with other countries.

-with AAP/ABC