Donald Trump has swept into Washington on a military jet as he kicked off three days of inaugural festivities, with the city braced for an onslaught of crowds and demonstrators.

Mr Trump was quickly taking on more of the trappings of the presidency, giving a salute to the Air Force officer who welcomed him as he stepped off the jet with wife Melania at Joint Base Andrews just outside Washington.

His first stop was a luncheon in a ballroom at his own hotel, where he gave a shout-out to Republican congressional leaders, declaring: "I just want to let the world know we're doing very well together."

House Speaker Paul Ryan, he said, will finally have someone to sign legislation into law.

Then Mr Trump veered into the territory of the unknowable to declare his cabinet selections had "the highest IQ".

Just streets away, the White House was quickly emptying out.

President Barack Obama's schedule was clear beyond his daily briefing and his final weekly lunch with vice president Joe Biden.

Vice President-elect Mike Pence, in a tweet, called Inauguration Eve "a momentous day before a historic day", as security barricades and blockades went up around Washington in preparation for Friday's swearing-in ceremony.

"We are all ready to go to work," Mr Pence said at a morning news conference.

"In fact, we can't wait to get to work for the American people to make it great again."

Outgoing Homeland Security secretary Jeh Johnson said he would be putting on his "favourite DHS jacket" and taking to the streets to inspect security preparations for the inaugural festivities.

He told MSNBC's Morning Joe that areas where inaugural crowds will congregate will be "extra fortified this year with dump trucks, heavily armoured vehicles to prevent anybody who's not authorised from being in the area from driving something in there".

He said there was "no specific credible threat" related to the inauguration.

Mr Trump's public schedule for the inaugural celebration starts with an afternoon wreath-laying at Arlington National Cemetery, followed by a welcome concert on the steps of the Lincoln Memorial ending with fireworks.

The two-hour concert, open to the public, was to feature country star Toby Keith, soul's Sam Moore, actor Jon Voight and The Piano Guys.

Also performing are Lee Greenwood, DJ RaviDrums, 3 Doors Down, and The Frontmen of Country, featuring Tim Rushlow, Larry Stewart and Richie McDonald.

They will not include singer Jennifer Holliday, originally announced as one of the headliners. She backed out after an outcry from Trump critics.

Before departing for Washington, Mr Trump announced his final cabinet choice: former Georgia governor Sonny Perdue for agriculture secretary.

Spokesman Sean Spicer said the president-elect was continuing to make "edits and additions" to the inaugural address he will deliver at Friday's swearing-in.

Mr Trump arrived on a Boeing 757 that is part of the fleet of military planes that become Air Force One whenever the president is aboard.

The president-elect, who flew to Washington without any press on his plane, was joined on the trip by a gaggle of his children, grandchildren and other members of his extended family.

Also spotted were bags of dresses and formal wear for the coming days' festivities.

At the luncheon, Mr Trump invited his future first lady to speak, and Melania Trump told the crowd: "Tomorrow we're starting the work," adding that "there's a lot of possibility and a lot to take care of".

Mr Trump made sure to work in a plug for his hotel, saying: "This is a gorgeous room. A total genius must have built this place."

Reporters covering Mr Trump's remark were removed from the room before the president-elect finished speaking.

Ebullient Trump fans were ready for a three-day party.

Jon-Paul and Jean Oldham, of Thomaston, Connecticut, visited the National Mall on Thursday and had seats for Friday's inauguration.

"We're hoping for good weather and hoping for some unity," said Jon-Paul Oldham, a firefighter and father of four.

He said everyone should want Mr Trump to succeed.

"Wanting him to fail is like wanting the plane to crash but you're on the plane," he said.

New York Republicans kicked off their inauguration festivities with a breakfast on Thursday morning at a central hotel.

The crowd, gathered in a ballroom to hear former House speaker Newt Gingrich, roared as New York party chairman Ed Cox boasted that a child from Queens was going to be the next president of the United States.

"It's going to be a remarkable couple of days," Mr Gingrich said.

"Certainly this is the inauguration that no-one in the news media was ready for."

He went on to describe Mr Trump as "part PT Barnum" and predicted he would be one of the country's most accomplished presidents.

It does appear it may rain on Mr Trump's parade.

Keeping a wary eye on the weather forecast for Inauguration Day, the National Park Service announced that it was easing its "no umbrella" policy for Friday, allowing collapsible umbrellas along the parade route and on the National Mall.