US President-elect Joe Biden has made a sober entrance to the nation's capital after delivering an emotional speech in his home state that paid tribute to his late son Beau.

Biden cried as he told a crowd of supporters in Wilmington, Delaware: "Excuse the emotion ... but when I die, Delaware will be written in my heart. And the hearts of all the Bidens ...

"I only have one regret - that [Beau's] not here, because we should be introducing him as president."

Biden spoke at the Major Joseph R. "Beau" Biden III National Guard/Reserve Centre, which was named for his eldest son, who died of brain cancer in 2015 at the age of 46. Beau Biden was a two-term Delaware attorney general and served in Iraq with the Delaware Army National Guard.

The President-elect had planned to take a train into Washington ahead of tomorrow's inauguration, but scratched that plan in the aftermath of the January 6 insurrection at the US Capitol.

He instead flew into a military base outside the capital and then motorcaded into the heavily barricaded city.

Outgoing President Donald Trump delivered another snub by forcing Biden to charter his own plane instead of authorising his use of an Air Force jet, the Daily Mail reports.

The Obama administration sent an Air Force plane to New York for the Trumps in January 2017.

Shortly before Biden departed for Washington, the US reached another grim milestone in the pandemic, surpassing 400,000 deaths from the virus, according to Johns Hopkins University.

"These are dark times," Biden told his supporters in Delaware. "But there's always light."

Biden, who ran for the presidency as a cool head who could get things done, plans to issue a series of executive orders on Day One — including reversing Trump's effort to leave the Paris climate accord, cancelling his travel ban on visitors from several predominantly Muslim countries, and extending pandemic-era limits on evictions and student loan payments.

Trump won't attend Biden's inauguration, the first outgoing president to skip the ceremony since Andrew Johnson more than a century and a half ago. The White House released a farewell video from Trump just as Biden landed at Joint Base Andrews.

Trump, who has repeatedly and falsely claimed widespread fraud led to his election loss, extended "best wishes" to the incoming administration in his nearly 20-minute address but did not utter Biden's name.

Vice President-elect Kamala Harris: "For many months we have grieved by ourselves. Tonight, we grieve and begin healing together." Photo / AP

Trump also spent some of his last time in the White House huddled with advisers weighing final-hour pardons and grants of clemency.

Trump plans to depart Washington today in a grand airbase ceremony that he helped plan himself.

After arriving in Washington, Biden went directly to an evening ceremony at the Reflecting Pool near the Lincoln Memorial to honour American lives lost to Covid-19. He was joined by Vice President-elect Kamala Harris, who spoke of the collective anguish of a nation.

"For many months we have grieved by ourselves," Harris said. "Tonight, we grieve and begin healing together."

Biden followed with his own brief remarks, telling Americans that "to heal we must remember". As he spoke with 400 lights representing the pandemic victims illuminated behind him, he faced the statue of Abraham Lincoln, the Civil War president who served as more than 600,000 Americans died.

Inaugural organisers this week finished installing some 200,000 US, state and territorial flags on the National Mall, a display to represent the American people who couldn't come to the inauguration, which is restricted under the tight security and Covid restrictions.

Ahead of Biden's arrival, 12 US Army National Guard members were removed from the presidential inauguration security mission after they were found to have ties with right-wing militia groups or posted extremist views online, according to two US officials. There was no threat to Biden, they said.