A US presidential campaign marked by upheaval and rancour approached its finale on Election Day as Americans decided whether to send Donald Trump back to the White House or elevate Kamala Harris to the Oval Office.

Voters faced a stark choice between two candidates who have offered drastically different temperaments and visions for the world’s largest economy and dominant military power.

Tens of millions of Americans cast early ballots – voting by post or in person prior to Tuesday.

Those voting on Election Day mostly encountered a smooth process around the country, with isolated reports of some hiccups that regularly happen, including long lines, technical issues and ballot printing errors.

Ms Harris, the Democratic vice president, stands to be the first female president if elected.

She has promised to work across the aisle to tackle economic worries and other issues without radically departing from the course set by President Joe Biden.

A political advertisement for Democratic presidential nominee Kamala Harris is displayed on the Sphere in Las Vegas (John Locher/AP)

Mr Trump, the Republican former president, has vowed to replace thousands of federal workers with loyalists, impose sweeping tariffs on allies and foes alike, and stage the largest deportation operation in US history.

The two candidates spent the waning hours of the campaign overlapping in Pennsylvania, the biggest battleground state.

They were trying to energise their bases as well as Americans still on the fence or debating whether to vote at all.

In Scranton, Pennsylvania, Liza Fortt arrived at her polling location in a wheelchair and not feeling well.

But she ventured out anyway to vote for Ms Harris.

Liza Fortt, centre, accompanied by her son Timothy Walker, left, and husband Willie Fortt, at a polling place at Scranton High School in Scranton, Pennsylvania (Matt Rourke/AP)

“It means a lot to me and my grandkids, my granddaughters, my nieces. … I was just waiting for this day to come,” said Ms Fortt, who is 74 and black.

She said she never thought she would have such an opportunity, to cast a ballot for a black woman in a presidential race.

“I’m proud, to see a woman, not only a woman, but a black woman,” Ms Fortt said.

Ms Harris and Mr Trump entered Election Day focused on seven battleground states, five of them carried by Mr Trump in 2016 before flipping to Mr Biden in 2020: the “blue wall” of Pennsylvania, Michigan and Wisconsin as well as Arizona and Georgia.

Nevada and North Carolina, which Democrats and Republicans respectively carried in the last two elections, were also closely contested.

The closeness of the race and the number of states in play raised the likelihood that once again a victor might not be known on election night.

Results are posted after the midnight vote on Election Day in Dixville Notch, New Hampshire (Charles Krupa/AP)

There was one early harbinger from the New Hampshire hamlet of Dixville Notch, which by tradition votes after midnight on Election Day.

Dixville Notch split between Mr Trump and Ms Harris, with three votes for each.

In the 2020 presidential race it took four days to declare a winner.

Regardless, Mr Trump has baselessly claimed that if he lost, it would be due to fraud.

Ms Harris’s campaign was preparing for him to try to declare victory before a winner is known on Tuesday night or to try to contest the result if she wins.

Four years ago, Mr Trump launched an effort to overturn the voters’ will that ended in the January 6 2021 insurrection at the US Capitol.

An image of Republican presidential nominee Donald Trump hangs in the window of a campaign office in Hamtramck, Michigan (David Goldman/AP)

Mr Trump planned to vote in his adopted home state of Florida on Tuesday, then spend the day at his Mar-a-Lago estate in advance of a party at a nearby convention centre.

Ms Harris has already voted by post in her home state of California.

She will have a watch party at her alma mater, Howard University in Washington.