(AFP) - US President Joe Biden was expected Thursday to unveil his administration's plans to tackle the coronavirus crisis, as he starts his first full day in the White House with America confronting a slew of challenges.

Biden was sworn in as the 46th US president on Wednesday, delivering a calming call to heal a nation riven by festering divisions that had grown deeper under four years of Donald Trump.

Biden took the presidential oath standing on the steps of the US Capitol, the building complex that had been attacked two weeks earlier by a pro-Trump mob seeking to overturn his victory. Moments earlier Kamala Harris had taken the oath to officially become America's first female vice president.

"Democracy is precious, democracy is fragile and at this hour, my friends, democracy has prevailed," Biden said before a National Mall that was virtually empty due to the ultra-tight security and a raging Covid-19 pandemic that he vowed to confront swiftly.

Absent from the ceremony was Trump, who had earlier left Washington for Florida, breaking 152 years of tradition by refusing to attend his successor's inauguration.

Trump has not publicly conceded defeat and spent the months since November's election falsely claiming he was cheated out of a second term.

Former presidents Bill Clinton, George W. Bush and Barack Obama did however attend the inauguration.

"I think if Americans would love their neighbor like they would like to be loved themselves, a lot of the division in our society would end," said Bush, a Republican.

Shortly after walking into the White House, his wife Jill by his side, Biden signed a flurry of executive orders, starting with rejoining the 2015 Paris climate accord from which the US withdrew under Trump.

"We are going to combat climate change in a way we have not done so far," the new US leader said, speaking in the Oval Office as he signed papers on the Paris deal which was negotiated when Biden was Obama's vice president.

Biden's spokeswoman Jen Psaki said his first call to a foreign leader would be Friday to Canadian Prime Minister Justin Trudeau -- after Biden blocked the Keystone XL pipeline fiercely opposed by environmentalists but backed by Ottawa.

Biden also halted the US exit from the World Health Organization, stopped construction of Trump's cherished wall on the Mexican border, and rescinded a ban on visitors from several Muslim-majority nations.

- A full in-tray -

Biden's presidency will initially be shaped by his response to Covid-19, which has killed more than 400,000 people in the US, and the associated economic emergency.

He will look to move quickly on coordinating a federal plan to combat the virus, which for months ran rampant across the country as the Trump administration bungled its response.

Biden is expected to outline his administration's plans later Thursday after he is briefed by his Covid-19 team.

Whereas Trump seldom acknowledged the tragic toll the virus was inflicting on Americans, Biden paused in his inaugural address to offer a moment's silent prayer for the victims.

The veteran Democrat also appealed to supporters of Trump, who shattered political norms by ruthlessly belittling rivals, denouncing entire ethnic groups and trying to cast doubt on basic facts.

"I will be a president for all Americans," Biden said.

Still, he confronted head-on the rise of domestic extremism, as evidenced during Trump's presidency by the Capitol assault, deadly attacks on synagogues and immigrants, and a violent march by neo-Nazis in Charlottesville, Virginia.

The United States faces "a rise of political extremism, white supremacy, domestic terrorism that we must confront, and we will defeat," Biden said.

Biden's inauguration ceremony, while steeped in pomp and tradition, was different from previous events, with no crowds and the National Mall closed.

Washington normally parties hard after an inauguration, but the US capital stayed quiet Wednesday.

A-listers made a valiant effort to keep up the energy at a mostly virtual, pre-produced show dubbed "Celebrating America."

At 78, Biden is the oldest-ever US president, a job he first sought in 1987, and is only the second Roman Catholic president after John F Kennedy.

Harris, the daughter of Indian and Jamaican immigrants, became the highest-ranking woman in US history, and the first Black person and first person of Asian heritage as the nation's number two.

She and her husband Doug Emhoff -- America's first-ever "second gentleman" -- were escorted to the inauguration by Eugene Goodman, a Black police officer at the Capitol who became a hero by luring away the mostly white mob away from the Senate chambers.

© Agence France-Presse