Polls in US battleground states began to close on Tuesday, inching the contest between President Donald Trump and Joe Biden to its nail-biting conclusion, following a race fought in unprecedented conditions of a global pandemic and the most deeply divided electorate in decades.

Soon after the polling time ended, AP reported that President Donald Trump had won Kentucky, and Democrat Joe Biden had carried Vermont. They were the first two states called in the 2020 presidential election. Trump won eight electoral votes from Kentucky, while Biden took three for winning Vermont.

What was not expected immediately was a definitive verdict on whether Trump gets another four years or Biden pushes him out of the White House.

Barring upsets in key states, that may not happen until all the swing states have counted their ballots — something that in the case of Pennsylvania could easily drag on at least into Wednesday.

Counting this year has been slowed by the unprecedented use of mail-in ballots in response to fears of the coronavirus. More than 100 million Americans had already cast votes before Election Day.

Trump, 74, expressed confidence as the evening approached, tweeting in all his characteristic all-caps “WE ARE LOOKING REALLY GOOD ALL OVER THE COUNTRY. THANK YOU!”

He was watching the results come in at the White House, surrounded by staff. It was not clear whether he'd speak to the public at some point but he said earlier Tuesday that he wasn't yet “thinking about a concession speech or acceptance speech.”

“Winning is easy,” he said. “Losing is never easy — not for me.”

Biden, hunkered down with family at home in Delaware, likewise said that voter patterns during the day seemed to favour his side.

“What I'm hearing is that there's overwhelming turnout. And overwhelming turnout particularly of young people, of women, and an overwhelming turnout of African American voters, particularly in Georgia and Florida, over the age of 65,” he told reporters.

“The things that are happening bode well for the base that has been supporting me.”

Robust turnout

With almost 102 million Americans voting early and millions more waiting in lines on Election Day, the rancorous campaign across a polarised nation clearly struck a nerve with the electorate.

“The most important issue is for us to set aside our personal differences that we have with each other,” said Eboni Price, 29, who rode her horse Moon to her polling place in a northwest Houston neighbourhood.

With the worst public health crisis in a century bearing down, the pandemic — and Trump's handling of it — became the inescapable focus for 2020.

Trump began the day on an upbeat note, predicting that he'd do even better than in 2016, but during a midday visit to his campaign headquarters, spoke in a gravelly, subdued tone.

“Winning is easy,” he told reporters. “Losing is never easy, not for me it’s not.”

In and around polling places across the country, reminders of a 2020 election year shaped by the pandemic, civil unrest and bruising political partisanship greeted voters.

Many wore masks to the polls either by choice or by official mandate with the coronavirus outbreak raging in many parts of the country.

After a summer of nationwide protests against police violence and racism, businesses in several major US cities were again boarded up as a precaution against unrest, an extraordinary sight on Election Day in the United States.

The American Civil Liberties Union and other civil rights groups said they were watching closely for signs of voter intimidation, and the US Justice Department's Civil Rights Division said it would deploy staff to 18 states.

Democratic presidential candidate Biden asked Americans to trust him as they had in 2008 and 2012 alongside Barack Obama. "We can heal the soul of this nation — I promise we won’t let you down," he tweeted.

Voters in Dixville Notch, a village of 12 residents in the US state of New Hampshire, kicked off Election Day at the stroke of midnight on Tuesday by voting unanimously for Biden.

The vote and count only took a few minutes, with five votes for Biden and none for President Donald Trump.

Polls began opening on the East Coast on Tuesday as election officials warned that millions of absentee ballots could slow the tallies, perhaps for days, in some key battleground states and as Trump threatened legal action to prevent ballots from being counted after Election Day.

Those yet to vote headed to polling places on Tuesday despite another spike in Covid-19 cases that has hit much of the country. Among those braving the polls were voters who may have wanted to vote by mail but waited too long to request a ballot or those who didn’t receive their ballots in time.

Election officials across some 10,000 voting jurisdictions scrambled to purchase personal-protective equipment, find larger polling places, replace veteran poll workers who opted to sit out this year’s election due to health concerns and add temporary workers to deal with the avalanche of mail ballots.

Later in the day, Trump again sought to sow doubt over the counting of ballots beyond election day, saying the country was “entitled” to know who won on the day of the vote.

“You have to have a date, and the date happens to be November 3,” he said during a visit to Republican National Committee offices in Arlington, Virginia.

“And we should be entitled to know who won on November 3.”

Biden leading in polls

More than 99 million Americans have cast their ballots in early voting, according to the US Elections Project.

The United States is more divided and angry than at any time since the Vietnam War era of the 1970s — and fears that Trump could dispute the result of the election are only fueling those tensions.

Despite an often startlingly laid-back campaign, Biden, 77, leads in almost every opinion poll, buoyed by his consistent message that America needs to restore its “soul” and get new leadership in the midst of a coronavirus pandemic that has killed more than 231,000 people.

Hours before the polling was to begin, Biden tweeted that he would "govern as an American president".

"I will work with Democrats and Republicans, and I’ll work as hard for those who don’t support me as for those who do."

“I have a feeling we're coming together for a big win tomorrow,” Biden said in Pittsburgh, Pennsylvania, a vital electoral battleground where he was joined by pop superstar Lady Gaga.

“It's time to stand up and take back our democracy.”

But Trump was characteristically defiant to the end, campaigning at a frenetic pace with crowded rallies in four states on Monday, and repeating his dark, unprecedented claims for a US president that the polls risk being rigged against him.

After almost non-stop speeches in a final three-day sprint, he ended up in the early hours of Tuesday in Grand Rapids, Michigan — the same place where he concluded his epic against-the-odds campaign in 2016 where he defeated apparent front-runner Hillary Clinton.

Despite the bad poll numbers, the 74-year-old Republican real estate tycoon counted on pulling off another upset.

“We're going to have another beautiful victory tomorrow,” he told the Michigan crowd, which chanted back: “We love you, we love you!”

“We're going to make history once again,” he said.

Warning of violence

There are worries that if the election is close, extended legal chaos and perhaps violent unrest could ensue — not least because Trump has spent months trying to sap public trust in the voting process in a nation already bitterly divided along political fault lines.

He ramped up these warnings in the final days, focusing especially on Pennsylvania's rule allowing absentee ballots received within three days after Tuesday to be counted.

In a tweet flagged with a warning label by Twitter on Monday, he said this would “allow rampant and unchecked cheating”.

“It will also induce violence in the streets. Something must be done!” Trump tweeted.