Donald Trump was elected US president, capping a remarkable comeback four years after he was voted out of the White House and ushering in a new American leadership likely to test democratic institutions at home and relations abroad.

Trump, 78, recaptured the White House yesterday after a campaign marked by dark rhetoric that deepened the polarisation in the country, prevailing after two attempts on his life and a late decision by Democrats to run Kamala Harris when President Joe Biden withdrew from the race in July.

Harris, the US vice president, called Trump to congratulate him for winning the 2024 presidential election, one of her senior aides said.

She is expected to deliver her concession speech around 6:00pm (2300 GMT).

The former president's victory in the swing state of Wisconsin pushed him over the 270 Electoral College votes needed to win the presidency. As of 8:00am ET (1300 GMT) Trump had won 295 electoral votes to Harris' 226 with only two states yet to be counted, Edison Research projected.

He also led Harris by more than 5 million votes in the popular count.

"America has given us an unprecedented and powerful mandate," Trump said early yesterday to a roaring crowd of supporters at the Palm Beach County Convention Centre in Florida.

Trump prevailed despite persistently low approval ratings. Impeached twice, he has been criminally indicted four times and found civilly liable for sexual abuse and defamation. In May, Trump was convicted by a New York jury of falsifying business records to cover up hush money payments to a porn star.

Trump's political career had appeared to be over after his false claims of election fraud led a mob of supporters to storm the US Capitol on January 6, 2021, in a failed bid to overturn his 2020 defeat.

But he swept away challengers inside his Republican Party and then beat Democratic candidate Harris by capitalising on voter concerns about high prices and what Trump claimed, without evidence, was a rise in crime due to illegal immigration.

Republicans also won a US Senate majority, but neither party appeared to have an edge in the fight for control of the House of Representatives where Republicans currently hold a narrow majority.

Major stock markets around the world rallied following Trump's victory, and the dollar was set for its biggest one-day jump since 2020.

Empty ground where supporters of Kamala Harris gathered for the election night watch party at Howard University, in Washington. Photo: Reuters

Voters identified jobs and the economy as the country's most pressing problem, according to Reuters/Ipsos opinion polls. Many Americans remained frustrated by higher prices even amid record-high stock markets, fast-growing wages and low unemployment.

With the Biden administration taking much of the blame, a majority of voters said they trusted Trump more than Harris to address the issues.

Hispanics, traditionally Democratic voters, and lower-income households hit hardest by inflation helped fuel Trump's election victory. His loyal base of rural, white and non-college educated voters again showed up in force.

World leaders from Europe to Asia congratulated Trump, whose victory will have major implications for US trade and climate change policies, the war in Ukraine, Americans' taxes and immigration.

Harris fell short in her 15-week sprint as a candidate, failing to galvanise enough support to defeat Trump, who occupied the White House from 2017-21, or to allay voters' concerns about the economy and immigration.

Harris had warned that Trump wanted unchecked presidential power and posed a danger to democracy.

Nearly three-quarters of voters say American democracy is under threat, according to Edison Research exit polls, underscoring the polarisation in a nation where divisions have only grown starker during a fiercely competitive race.

Trump ran a campaign characterised by apocalyptic language. He called the United States a "garbage can" for immigrants, pledged to save the economy from "obliteration" and cast some rivals as the "enemy within."

His diatribes were often aimed at migrants, who he said were "poisoning the blood of the country," or Harris, whom he frequently derided as unintelligent.

Despite legal woes and controversies, Trump is only the second former president to win a second term after leaving the White House. The first was Grover Cleveland, who served two four-year terms in the late 1800s.