Biden sworn in as 46th US president without a hitch, mandating masks as his first order of business.

Democrat Joe Biden has been sworn in as President of the United States, vowing to end the "uncivil war" in a deeply divided country reeling from a battered economy and a raging coronavirus pandemic.

With his hand on a 12cm-thick heirloom Bible that has been in his family for more than a century, Biden took the oath of office administered by US Chief Justice John Roberts that binds the president to "preserve, protect and defend the constitution of the United States".

"Through a crucible for the ages, America has been tested anew, and America has risen to the challenge," Biden said in his inaugural address.

"Today we celebrate the triumph not of a candidate but of a cause: the cause of democracy... At this hour, my friends, democracy has prevailed."

President Joe Biden urged Americans to "join forces, stop the shouting and lower the temperature" in his Inauguration speech. Watch: pic.twitter.com/NuW9rrwImv

— Vox (@voxdotcom)

Biden, 78, became the oldest US president in history at a scaled-back ceremony in Washington DC that was largely stripped of its usual pomp and circumstance, due both to the coronavirus and security concerns following the January 6 assault on the Capitol by supporters of outgoing President Donald Trump.

There is no time to waste when it comes to tackling the crises we face. That's why today, I am heading to the Oval Office to get right to work delivering bold action and immediate relief for American families.

— President Biden (@POTUS)

Top Republicans, including Vice President Mike Pence and the party's congressional leaders, attended Biden's inauguration, along with former US presidents Barack Obama, George W. Bush and Bill Clinton.

Biden's running mate, Kamala Harris, the daughter of immigrants from Jamaica and India, became the first black person, first woman and first Asian American to serve as vice president after she was sworn in by US Supreme Court Justice Sonia Sotomayor, the court's first Latina member.

Biden takes office at a time of deep unease, with the country facing what his advisers have described as four compounding crises: the pandemic, the economic downtown, climate change and racial inequality.

He has promised immediate action, including a raft of executive orders on his first day in office.

In his first official act as president, Biden signed an executive order, mandating masks.

After a bitter campaign marked by Trump's allegations of election fraud, Biden struck a conciliatory tone, asking those who did not vote for him to give him a chance to be their president as well.

"To overcome these challenges to restore the soul and secure the future of America requires so much more than words. It requires the most elusive of all things in a democracy: unity," he said.

"We must end this uncivil war that pits red against blue, rural versus urban, conservative versus liberal. We can do this - if we open our souls instead of hardening our hearts."

It's an honor to be your Vice President. pic.twitter.com/iM3BxJzz6E

— Vice President Kamala Harris (@VP)

Instead of a throng of supporters, the National Mall on Wednesday was covered by nearly 200,000 flags and 56 pillars of light meant to represent people from US states and territories.

Performers included Lady Gaga and Jennifer Lopez, and Amanda Gorman has become the youngest inaugural poet in US history at the age of just 22, delivering her poem "The Hill We Climb".

Watch Amanda Gorman, the youngest inaugural poet in U.S. history, recite her poem “The Hill We Climb” at President Biden's inauguration. https://t.co/5yi8RThWd9 pic.twitter.com/JcVuOhOU4h

— The New York Times (@nytimes)

At President Biden’s inauguration, Lady Gaga performed “The Star-Spangled Banner.” https://t.co/4gGKCue25u pic.twitter.com/rwUUtb7ICa

— The New York Times (@nytimes)

Trump skips inauguration, hints of return.

The norm-defying Trump flouted one last convention on his way out of the White House when he refused to meet with Biden or attend his successor's inauguration, breaking with a political tradition seen as affirming the peaceful transfer of power.

He is the first president to snub his successor's inauguration since 1869.

Trump did not mention Biden by name in his final remarks as president on Wednesday morning - before boarding Air Force One for the last time and headed to his Mar-a-Lago retreat in Florida.

President Trump at farewell ceremony: “I wish the new administration great luck and great success. I think they’ll have great success. They have the foundation to do something very spectacular.” https://t.co/z4kBh5v9lm pic.twitter.com/Tee6Zj9Uav

— ABC News Politics (@ABCPolitics)

"It is my greatest honour and privilege to have been your president," Trump said at Joint Base Andrews in Maryland after leaving the White House for the last time.

"I wish the new administration great luck and great success. I think they'll have great success, they have the foundation to do something really spectacular."

Trump told his cheering, chanting supporters that he'll be watching and listening from a distance.

"So just a goodbye. We love you," he said. "We will be back in some form."

First lady Melania Trump spoke at President Trump's final farewell ceremony at Joint Base Andrews https://t.co/i0UQqQS6s9 pic.twitter.com/onaG7B4i73

— CNN Breaking News (@cnnbrk)

US President Donald Trump has followed at least one presidential tradition.

The White House says the Republican president left behind a note for his successor. But deputy press secretary Judd Deere declined to reveal what Trump wrote to Biden or to characterise the sentiment in the note, citing privacy for communication between presidents.

Pence applauds Harris at inauguration.

Outgoing US Vice President Mike Pence and his wife Karen have attended the inauguration of new President Joe Biden after skipping both a farewell ceremony for Donald Trump and the usual protocol of welcoming his successor to his home at the Naval Observatory.

Pence, whom some of Trump's supporters during the deadly January 6 assault on the US Capitol had threatened to hang for refusing to try to overturn Biden's Electoral College win in Congress, applauded the next vice president, Kamala Harris, as she arrived at the US Capitol.

Vice President Harris and her husband Doug Emhoff escorted former Vice President Mike Pence and his wife Karen Pence down the steps of the US Capitol after the inauguration ceremony https://t.co/qNDfmZZIju pic.twitter.com/iZC9xn4hFo

— CNN (@CNN)

The couple plans to move back to Indiana later this year.

Pence was a loyal lieutenant throughout Trump's four-year term. But he found himself shunned by the outgoing president for days for not supporting his quest to overturn Biden's victory based on claims of voting fraud and irregularities, although the two men sought to repair their ties before leaving office.

Pence spoke with Harris last Thursday, marking the highest-level known contact between the outgoing and incoming administrations.

UK records deadliest day of pandemic.

The UK has recorded its deadliest day in the coronavirus pandemic, as the nation's chief scientist warns parts of the nation's health system are like a "war zone".

Official figures showed January 12 had the highest number of deaths recorded on a single day, with 1110 COVID-19 fatalities, eclipsing the previous peak of 1073 on April 8, 2020.

A record 1820 further deaths within 28 days of testing positive for COVID-19 were also reported on Wednesday, although there is a time lag between a patient dying and appearing in the statistics.

UK records new daily high of 1,820 Covid deaths, the highest number since the pandemic began https://t.co/TJi6DODAOw

— BBC Breaking News (@BBCBreaking)

The grim statistics appeared as authorities gave a stark warning about the strain the pandemic was putting on UK hospitals.

"This is very, very bad at the moment, with enormous pressure, and in some cases it looks like a war zone in terms of the things that people are having to deal with," Chief Scientific Advisor Sir Patrick Vallance said.

There was "light at the end of the tunnel" in the form of the vaccination programme, which has so far helped 4,609,740 people receive a first jab.

But Sir Patrick warned that vaccines were not doing enough of the "heavy lifting" at the moment to consider easing lockdown restrictions in Britain.

"You go for a walk in the park or something, life looks normal. You go for a walk in a hospital, if you work in a hospital, you will see life not looking normal at all," he toldSky News.

Australian leaders told to solve virus border battles.

Australia's leaders are again being urged to develop a uniform approach to domestic border rules, nearly one year into the coronavirus pandemic.

No areas of Australia qualify as a COVID-19 hotspot under the federal government's definition after it was lifted for Sydney's Northern Beaches last week.

The Commonwealth's hotspot definition is met when there is an average of 10 coronavirus cases a day over three days in metropolitan areas, and three a day in regional parts of Australia.

There have been no cases of local transmission of the virus across the country for three days.

But some Sydney residents still can't travel to Queensland and Victoria, while Western Australia continues to keep up its border with all of NSW.

An easing of restrictions in New South Wales as early as next week has infectious disease experts warning that it's too soon for such a major step forward. #9Today pic.twitter.com/M8kB6M0VSw

— The Today Show (@TheTodayShow)

While Australians seek consistency and clarity on domestic travel, state leaders have this week traded barbs over their differing approaches to the virus.

The issue will be canvassed at Friday's national cabinet meeting of Prime Minister Scott Morrison and state and territory leaders.

A group of NSW and Victorian MPs have written to him urging that the meeting adopt a uniform policy on border closures and compensate affected businesses.

Djokovic hits back at his Open critics.

World No.1 Novak Djokovic insists he was not being "selfish, difficult and ungrateful" in speaking out about quarantine conditions for players ahead of the Australian Open.

Ten people who have flown to Melbourne for the first grand slam of the year