Millions of Americans are voting in an historic election that could put Donald Trump back into the White House or make Kamala Harris the first woman to become US president.

The two candidates are neck and neck in the polls after bitter campaign that saw two assassination attempts against Republican Mr Trump as well as the shock withdrawal of President Joe Biden.

In around 100 days, Ms Harris has found her feet and mounted a fierce challenge to her opponent.

With just hours left before polls close, the election has come down to the wire and could be decided by a handful of crucial battleground states.

Follow live: Harris makes surprise stop in Washington

Voting on Tuesday appears to be smooth, with only scattered reports of delays from extreme weather, long lines or technical problems.

The FBI reported that there had been “non-credible” bomb threats to several states, some of which it said came from Russian email domains.

How the vote works

As well as those lining up at polling booths on Tuesday, tens of millions of Americans cast early ballots – voting by post or in person before today.

To become president, the winning candidate needs 270 electoral votes or more, with each state carrying a different number of votes.

If the polls predicting a close race are correct, the election will likely come down to a few battleground states: Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin.

The first ballots cast on Tuesday mirrored the national divide. Overnight, the six registered voters in the tiny hamlet of Dixville Notch, New Hampshire, split their votes between the two candidates in voting just past midnight.

Read more:
An easy guide to the US election
What Trump or Harris victories would mean for UK

Trump or Harris

Former President Mr Trump, 78, voted in Palm Beach, Florida, near his Mar-a-Lago club.

Wearing his trademark red “Make America Great Again” baseball cap, he said at the polling station that he was feeling “very confident”.

“I hear we’re doing very well,” he said. “It looks like Republicans have shown up in force.”

Elon Musk, the world’s richest man and Trump donor, said he will watch results unfold with the former president.

In the meantime, Ms Harris, the 60-year-old Democratic vice president, did radio interviews in the battleground states of Pennsylvania, Georgia and North Carolina.

What do the polls say?

Many polls are too tight to call and, with a large margin of error, most experts are refusing to predict the outcome.

Georgia could be among the first battleground to declare, with polls there closing at 7pm local time (midnight UK time). State election officials told Sky News they could have a result as early as 10pm (3am UK time).

Follow Sky News on WhatsApp

Keep up with all the latest news from the UK and around the world by following Sky News

Tap here

North Carolina could also give an early indication of how the vote is going.

Even so, it could be several days before the US has a definitive result.

An exit poll by conducted today by Sky News’ sister outlet NBC News and other US outlets suggests that democracy is the top issue on the minds of voters as they cast their ballots.

Some 35% of people said it was their most important issue, closely followed by the economy on 31% and with abortion ranked third at 14%.

Voters are not just selecting a president. A number of seats in the House of Representatives and the Senate are up for grabs. In addition, 10 states will hold abortion-related ballots, half of which would overturn existing restrictions.

Voters across 50 states are preparing to cast their ballots after a bitterly contested US election campaign, which will see Donald Trump or Kamala Harris become president.

In the last few hours, both candidates have been giving their final pitches. “The momentum is on our side,” Ms Harris told a crowd in Philadelphia that chanted back, “We will win”.

“Tonight, then, we finish as we started: with optimism, with energy, with joy,” she said, while enjoying the support of celebrity endorsements on the day from Katy Perry, Lady Gaga and Jon Bon Jovi.

US election latest updates

In contrast, Mr Trump ended his campaign in Michigan, repeating key messages about the economy and immigration.

A handful of states will play a crucial role in determining the outcome of the election. Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin hold the keys to the White House.

To become president, the winning candidate needs 270 electoral votes or more, with each state carrying a different number of votes.

But the focus has been on Pennsylvania which carries 19 electoral votes, the most of all the swing states.

It has been a remarkable journey for both candidates – with Mr Trump surviving two assassination attempts and Ms Harris not even originally in the running.

For more than a year, the 2024 presidential race seemed destined for a rematch between Joe Biden and Mr Trump – but a disastrous TV debate by Mr Biden eventually forced him to withdraw from the ticket.

The Democratic party’s decision to replace Mr Biden with his vice president transformed the race and shifted polls in Ms Harris’s favour. But only just.

Many polls are too tight to call and, with a large margin of error, most experts are refusing to predict the outcome.

Read more:
Overseas ballots face legal challenge
You decide the new president
Should we fear Trumponomics?

Later, attention will turn to those battleground states including Georgia, which is among the first polls to close at 7pm local time (midnight UK time).

State election officials told Sky News they could have a result as early as 10pm (3am UK time).

Even so, it could be several days before the US has a definitive result.

Voters are not just selecting a president. In addition, 10 states will hold abortion-related ballots, half of which would overturn existing restrictions.

Predict who you think will win in each swing state and we’ll tell you who the president will be if you’re right.

Tonight, Sky News will have access to the most comprehensive exit poll and vote-counting results from every state, county and demographic across America through its US-partner network NBC.

You can find out more about Sky News’ coverage here.

Up to 4,000 people voting overseas in the US election are having their ballots challenged in Pennsylvania, a key battleground state, according to the American Civil Liberties Union (ACLU).

They include Selma Aldi, 47, from Camden in north London who received a letter on Sunday explaining that her ballot in the US presidential election is at risk of being rejected.

“It was a shock,” she said. “It was terrifying to be targeted, to potentially lose a right that I hold as very important. It’s even a feeling that someone is questioning my identity.”

Latest on US election

The trainee GP, who grew up in Hershey, Pennsylvania left America in 2000 but has voted via absentee ballot in every US presidential election since.

A letter from election officials in Dauphin County outlines the legal challenge. It reads: “The applicant is not registered to vote and therefore is not eligible to vote in Pennsylvania.

“Under Pennsylvania law, it is a felony to permit any person to vote who is not registered.”

A hearing on the legal challenge is scheduled for Friday, in which Ms Aldi can respond.

Around 2.8 million US citizens living abroad are entitled to vote in the election, no matter where they are on polling day.

But each state has different procedures and rules on how election paperwork can be sent and received.

But Ari Savitzky, senior staff Attorney at the ACLU said “any attempt to challenge [voters] eligibility is a clear violation of their rights”.

He told Sky News: “Between 3,000 and 4,000 challenges have been filed in Pennsylvania to the absentee ballots of US citizens living abroad.

“For decades, federal law has guaranteed the right of US citizens living abroad to vote in federal elections at their last US residence.

“In addition to being legally baseless, these challenges are an abuse to voters and to election administrators.”

Read more from Sky News:
US election: Colleges, swing states and how it all works
Should we fear Trumponomics?
What happens if there’s a tie in the US election?

Deborah Hinchey from another voting rights group, All Voting is Local, said: “Election deniers across Pennsylvania have submitted thousands of mass challenges to overseas voters.

“They want to block as many ballots as possible and silence our voices… but these baseless challenges have failed before and the proper checks and balances are in place to make sure they’ll fail again,” she added.

Tonight, Sky News will have access to the most comprehensive exit poll and vote-counting results from every state, county and demographic across America through its US-partner network NBC.

You can find out more about Sky News’ coverage here.