After a night of gripping results in which each candidate ran neck-and-neck in tight races, the final result of the US election is unlikely to be known for many hours or even days.
As voters await the results of the presidential race between Donald Trump and Joe Biden, questions have been raised about the possibility of a tie.
But could a tie really take place and what would happen then? Sky News explains.
How are the votes counted?
All 50 states have a central election authority, but the ballots are processed by dozens of separate county or municipal election offices.
Most require a signature and witness but some states allow voters to get around this by signing an affidavit. How that is applied can be decided on a local level, and how far officials go to contact the voter is up to them.
Republicans and Democrats have begun legal action in key states to try and extend mail-voting deadlines, or to cut them back.
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Why might there be a delay in the result?
In many states – including battleground states Michigan, Pennsylvania, Wisconsin and North Carolina – officials will count ballots that arrive after 3 November, as long as they are postmarked by election day.
But whether or not the ballots are counted depends on how local election workers enforce rules, notify voters and whether they allow errors to be fixed.
A close count in key battleground states could even result in litigation over voting and ballot counting procedures.
Could there be a tie for the presidency?
With there being an even number of electoral votes, this is a possibility.
After a flurry of states reported their results during the early hours of Thursday, Mr Biden was on 220 votes, compared to Mr Trump’s 213, as of 6.40am.
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The remaining Electoral College votes leave several routes for either candidate to win the election – or for the poll to end in a tie.
If Mr Biden wins all the states won by then-Democratic nominee Hillary Clinton in 2016, and gains Michigan, Wisconsin and Arizona, both he and Mr Trump would end up on 269 votes.
A tie would also arise if Mr Biden wins everything that Mrs Clinton did, plus Michigan and Pennsylvania – after he won one of Nebraska’s five electoral votes.
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What happens if the result is a tie?
The newly-elected House of Representatives would choose the president, while the Senate would be tasked with choosing the vice president.
The Constitution’s 12th Amendment, which spells out how the president and the vice president are elected, stipulates that the House vote for president be taken according to state delegations – as in one vote per state.
A simple majority of states, equivalent to 26 votes or more, would be needed to win.
A tie has not been seen in modern times but the process was implemented in the 1800s, including in the election of 1800 between Thomas Jefferson and Aaron Burr.
What happened the last time the result wasn’t clear?
In 2000, George W Bush was only confirmed as the winner of the election following a Supreme Court ruling a month after the election, following a number of recounts. The state had been called for both Mr Bush and Al Gore at various points.
In the end, Mr Bush prevailed over Mr Gore by just 537 votes in Florida. That is the only time the court has decided the outcome of a US presidential election.
Amy Coney Barrett’s confirmation as a Supreme Court justice following the death of Ruth Bader Ginsburg, created a 6-3 conservative majority in America’s highest court, which could favour Mr Trump if it is required to weigh in on a contested election.
Will it all end up in court this time?
Mr Trump has claimed the result of the 2020 election could be settled by the Supreme Court but Mr Biden has said he will accept the result.
The incumbent has alleged “a fraud on the American public” and told supporters that he would take it to the Supreme Court.
Both sides have assembled vast legal teams to advise the two campaign teams on potential challenges, particularly in the key swing states.
The Democrats have warned for months that Mr Trump will try to “steal” the election by challenging results in the battleground states on voter fraud claims – and Mr Trump has thrown the allegation back at the Democrats in a tweet.
Legal challenges could go on for weeks.