Vote results are filtering through in the US Election with the race between President Donald Trump and Democrat challenger neck and neck.
Mr Trump claimed swing state Florida giving him a vital victory, while Biden has all but flipped Republican state Arizona.
Though counting in many states has concluded it could be days before a victor is known.
How will election night unfold?
On election night (November 3) polls began closing on the east coast of the country at 7pm (midnight UK time).
A running total of votes has been counted for each state, with news networks “calling” a state when a candidate is believed to have an unassailable lead. This is just a prediction, however, not an official result.
The winners of a state are assigned a number of “electoral votes” if they claim a state, depending on the population of the state, with the victor requiring 270 votes.
In 2016 the first results were known just after midnight (GMT). The results in the key swing states of Ohio and Florida, were known just prior to 4am
On the morning of November 4 the loser of the election will likely make a public concession to the public to make it clear who has won.
In the days after the vote local officials will finish counting the ballots and send the results to state officials who then approve them and send them onto federal officials
When will we know the US Election winner?
Typically, the winner of the election is known on election night itself.
In 2016 Donald Trump was announced as the projected winner at about 7.30am GMT the morning after the election when he clinched the 10 electoral college votes of Wisconsin.
It could however be weeks or months before a winner is known, due to the ongoing coronavirus pandemic.
With postal voting now widely permitted in most states, with the number of postal ballots expected to double at the 2020 vote.
The US postal service has been subject to severe cutbacks under the Trump administration and there are fears that they may be unable to cope with the increased volume of votes.
Postal votes can take longer to count, while rules vary on a state-by-state basis over when a postal vote needs to arrive by.
There are also concerns about delays at polling stations on election day with fewer polling stations than usual set to be open and fears of worker shortages.
States are required to have settled election disputes by December 8, known as the "safe harbor deadline." Congress can refuse to accept the electoral votes from that state if the deadline is not met.
Will the loser accept defeat?
If the vote is a close fought one there are also concerns that the loser will refuse to accept defeat.
Mr Biden has said that he will accept the full results, but indicated that he may not concede immediately when he stated: “Count every vote."
Mr Trump meanwhile has refused to commit to a peaceful transfer of power, saying that there could be "tremendous fraud" due to postal votes - an argument with little substance.