Donald Trump claimed on Wednesday morning he was winning Pennsylvania by a “tremendous amount” with the fate of both campaigns hanging on the key state.
With 77 per cent of votes counted, Mr Trump leads Mr Biden by 54.3 per cent to 44.3 per cent.
However, Democrats pointed to the fact that the state’s postal vote count was not complete, with Joe Biden expected to pick up a majority of those votes in the state.
In Pennsylvania, ballots postmarked by Nov 3 can be accepted if they arrive up to three days after the election.
The state carries 20 electoral college votes, which both camps are relying on to get over the 270-vote mark needed to win the election.
In his address in the early hours of Wednesday morning, Mr Trump said he was asking the Supreme Court to suspend the count.
Pennsylvania’s Democratic Governor Tom Wolf called Mr Trump’s unsubstantiated claim about fraud in the US presidential election a “partisan attack”, and said his state was working hard to count more than 1 million mail-in ballots.
“Let’s be clear: This is a partisan attack on Pennsylvania’s elections, our votes, and democracy,” Wolf said in a tweet. “Our counties are working tirelessly to process votes as quickly AND as accurately as possible. Pennsylvania will have a fair election and we will count every vote.”