Donald Trump pronounced the start of a "golden age" in the United States after taking the oath for a historic second term as president on Monday, using his inaugural speech to lash out at what he described as a "broken" society that he would rescue.

"The golden age of America begins right now. From this day forward our country will flourish and be respected again all over the world," Trump said in the US Capitol, where his inauguration was held indoors due to chilly weather.

While promising renewal, Trump's tone was characteristically dark, denouncing what he said had been a "betrayal" of Americans by a "radical and corrupt establishment."

"For many years, a radical and corrupt establishment has extracted power and wealth from our citizens, while the pillars of our society lay broken and seemingly in complete disrepair," he said.

"From this moment on, America's decline is over."

The Republican — at 78 now the oldest person ever to take the presidential oath — was set to kickstart his new term with a blitz of immediate orders on immigration and the US culture wars.

"I will declare a national emergency at our southern border" with Mexico, Trump said to loud cheers from supporters inside the ornate Rotunda hall, vowing to deport "millions and millions" of illegal immigrants.

Trump took the oath with one hand raised in the air, using a Bible given to him by his mother, and became the 47th president.

He had traveled to the Capitol with outgoing Democratic president Joe Biden, who followed tradition by offering his successor tea at the White House.

"Welcome home," Biden had said to Trump as he and First Lady Jill Biden greeted the incoming president and his wife Melania at the White House.

Trump was a political outsider at his first inauguration in 2017 as the 45th president, but this time around he is surrounded by America's wealthy and powerful.

The world's richest man, Elon Musk, Meta boss Mark Zuckerberg, Amazon chief Jeff Bezos and Google CEO Sundar Pichai all had prime seats in the Capitol alongside Trump's family and cabinet members.

Musk, who bankrolled Trump's election campaign to the tune of a quarter of a billion dollars and promotes far-right policies on the X social network, will lead a cost-cutting drive in the new administration.

While Trump refused to attend Biden's 2021 inauguration after falsely claiming electoral fraud, this time Biden has been keen to restore the sense of tradition.

Biden joined former presidents Barack Obama, George W. Bush and Bill Clinton at the Capitol. Former first ladies Hillary Clinton and Laura Bush were there but ex-first lady Michelle Obama pointedly stayed away.

Executive orders

Unusually for an inauguration where foreign leaders are normally not invited, Argentina's hard-right president Javier Milei was attending, along with Italy's far-right Prime Minister Giorgia Meloni.

The bitter cold weather has forced Trump's inauguration indoors for the first time since Ronald Reagan's in 1985, missing out on the customary massive crowds along the National Mall.

Behind the pomp and ceremony, the billionaire is kickstarting his nationalist, right-wing agenda with a barrage of around 100 executive orders undoing Biden's legacy.

Trump will give the US military a key role on the frontier, and end birthright citizenship, as he seeks clamp down on undocumented migrants, an official from his incoming administration said.

He will also sign an order for the US government to recognize only two biological sexes and seek to eliminate federal government diversity programs as he takes office.

'Ecstatic'

At sunrise on Monday, the National Mall, where the inauguration was due to be held, was largely empty — save for the Fairchild family, who traveled from Michigan to pay tribute to Trump.

"Ecstatic," said grandmother Barb, when asked how they were feeling, adding she thought the move indoors was made "to protect our president."

With minutes left in his presidency, Biden issued extraordinary pre-emptive pardons for his brothers and sister to shield them from "baseless and politically motivated investigations."

He also pardoned former Covid-19 advisor Anthony Fauci, retired general Mark Milley, and members of a US House committee probing the violent January 6, 2021 US Capitol attack by Trump's supporters.

Biden said he had also restored the tradition of leaving a letter for his successor — though he said the contents were between him and Trump.

Trump is just the second president in US history to return to power after being voted out, after Grover Cleveland in 1893.

Another notable factor is Trump's criminal record, related to paying a porn star hush money during his first presidential run — and a string of far more serious criminal probes that were dropped once he won the election in November.

For the rest of the world, Trump's return means expecting the unexpected.

From promising sweeping tariffs, to making territorial threats to Greenland and Panama and calling US aid for Ukraine into question, Trump looks set to rattle the global order once again.

Russian President Vladimir Putin congratulated Trump ahead of the inauguration and said Monday he was open to talks on the Ukraine conflict, adding he hoped any settlement would ensure "lasting peace."

AFP