The United States looks set for a nail-biting conclusion to the 2020 presidential election with the race to 270 electoral college votes too close to call.

As predicted by most pollsters, the result is hinging on tightly-fought contests in crucial swing states.

One of these purple states is Pennsylvania which could well play kingmaker this election.

Vote counting could take days in Pennsylvania (Getty Images)

Complications caused by unprecedented mail-in voting, however, means that it could be some time before it is known how the rust belt states voted.

When was the result declared in 2016?

The result in Pennsylvania wasn’t known until roughly 7.30am UK time in 2016.

Trump clinched the Rust Belt state, securing his victory minutes later with a victory in Wisconsin.

When will the result be declared in 2020?

It could be some time before the result is called in all three states, with counting expected to carry on well beyond election night.

The slow count is due to the millions of Americans who have opted to vote by mail due to the coronavirus pandemic.

Generally speaking mail-in votes take longer to count, and in Pennsylvania, the processing of absentee ballots didn’t take place until Election Day morning, with ballots postmarked before Nov. 3 but received after Election Day eligible to be counted.

The state isn’t expected to have finished counting until Friday – so if the race becomes a matter of votes, it might not be until Friday that we have a result. If a clear frontrunner emerges a victor will be declared far earlier.

Who is favourite to win the states?

As of 9.30am GMT on Thursday morning Trump holds a slender lead in Pennsylvania by 3,215,983 to 3,051,565, though with mail-in voting supposedly dominated by the Democrat vote that margin of victory will likely narrow.

Pennsylvania election result 2020: when will results from the swing state be known - and why is it crucial for Trump and Biden?