As of midnight on Wednesday, the state remained too close to declare a winner, with Trump leading by 176,498 votes and more than 763,311 absentee ballots yet to be counted, according to election officials.
Voting in Philadelphia and Pittsburgh was temporarily halted on Thursday because of his ongoing court battles.
Data released on Wednesday from the Pennsylvania Secretary of State shows that Biden so far leads Trump in tallied absentee ballots there by a margin of 77 per cent to 23 per cent.
If he carried the remaining absentee ballots by a similar margin, Biden would bring in 419,000 more additional votes than Trump, enough to overcome his current deficit, according to a DailyMail.com analysis.
In Pennsylvania and most other states, in-person voting on Election Day solidly favored Trump -- but the Republican incumbent has seen his early lead whittled away as the mail-in ballots are tallied.
Compounding the confusion, Pennsylvania is one of several states that did not begin counting absentee ballots until Election Day -- leading to a huge backlog after the state received a record 2.6 million mail-in votes.
Luzerne County employees open mail-in ballots to be counted at the elections board in Wilkes-Barre, Pennsylvania on Wednesday. Trump's lead in the state narrowed as votes were counted
National Guard troops assemble near a Target store in Philadelphia, Pennsylvania Wednesday
Pennsylvania also continues to accept absentee ballots until 5pm on Friday, provided that they are postmarked on or before Election Day.
It has led the Trump camp to cry foul, and Trump has filed suit to stop the counting of ballots in Pennsylvania that are received after Election Day, and seeking better access for campaign observers to locations where ballots are being processed and counted.
Trump dispatched his son Eric and personal attorney Rudy Giuliani to Pennsylvania as his legal emissaries on Wednesday.
At a press conference, Giuliani ranted for several minutes about mail-in ballots, which he claimed without proof could be falsified.
'This is beyond anything I have ever seen before,' he said. 'Do you think we're stupid? Do you think we're fools?
'You know something, Democrats do think you're stupid,' Giuliani added. 'And they do think you're fools. That's why you get called 'deplorable' and 'chumps'.
'We're going to stick with this. We're going to win this election. We've actually won it. It's just a matter of counting the votes fairly.'
Giuliani complained the mail-in ballots could have come from Mars or Canada – or could simply be one person who sent in 100,000 votes.
'Do you think we're stupid? Do you think we're fools?' Giuliani claimed of the vote count
Pennsylvania Governor Tom Wolf, a Democrat, blasted Trump's lawsuit as an attempt to 'subvert the democratic process'.
'We’ve seen efforts across the country to undermine this election, including a lawsuit from the Trump campaign to block the counting of ballots — the counting of your vote. This goes against the principles of our democracy and the right of every American citizen,' Wolf said in a tweet.
'Our election officials should be free to do their jobs without intimidation or attacks. These attempts to subvert the democratic process are disgraceful. Let me be clear: Pennsylvania is going to count every vote and make sure your voice is heard,' Wolf added.
The governor vowed to 'fight like hell to protect your vote.'
Republican state officials are also trying to cast doubt on the state’s election process.
Late Tuesday, the two most prominent Republicans in the Pennsylvania Senate issued a 1,500-word press release criticizing the state’s top election official and accusing her of mishandling the election.
Pennsylvania’s Senate Majority Leader Jake Corman and Senate President Pro Tempore Joe Scarnati blasted Secretary of State Kathy Boockvar, a Democrat, saying she had changed her guidance to counties multiple times in the days leading up to Election Day. The also called for Boockvar to resign.
Wolf issued strongly worded rebuke to the Republican leaders, calling their criticism 'an attempt to undermine confidence in the results of the election' and adding that 'we should all denounce them for the undemocratic actions they are.'
Pennsylvania Governor Tom Wolf, a Democrat, blasted Trump's lawsuit as an attempt to 'subvert the democratic process'
Pennsylvania (pictured, Philadelphia) is being watched closely as the fate of the presidency could come down to the state bordering New York
'I support our Secretary of State and all of our state and local election officials who are working hard to deliver timely, accurate results and ensure that everyone's vote is counted and protected,' Wolfe continued.
Boockvar told reporters she will not be resigning, and instead cast blame at the legislature, which is in fact to blame for the delay in counting mail ballots.
The protests of Corman and Scarnati were based in-large on two main issues.
They complained that Boockvar’s instructions about how to handle mail ballots that arrived after 8pm on Election Day could lead to these ballots getting mixed up with ballots that arrived before that hour.
The difference between the two groups is that any mail ballot that arrived before 8pm on Election Day would be counted regardless. It's believed there are between 2.5 to 3 million requested mail ballots that fall into this group.
There is a pending Republican appeal at the Supreme Court over whether Pennsylvania can count votes that arrive in the mail from Wednesday to Friday.
Republicans had also filed suits in state and federal court on Tuesday challenging Pennsylvania election officials’ move to allow counties to contact voters whose mail-in ballots were rejected because of mistakes, and then give them the opportunity to fix those ballots or cast provisional, replacement ballots.
In their joint letter, Corman and Scarnati also touched upon this issue.
Boockvar previously issued instructions to counties saying they could allow a voter to cast a provisional ballot if there was a problem with their mail ballot. Not all counties did this, however, and so Republicans claim the decision is being carried out unequally.
'This scattershot approach to Pennsylvania’s elections is wholly inappropriate and a direct breach of the positions she is on record of supporting in litigation – a position that Justice Baer specifically said is best left to the legislative branch of Pennsylvania’s government,' Corman and Scarnati wrote.
'As leaders, we simply cannot stand by and allow Kathy Boockvar’s blatant disregard for the legislative process and the law to continue.
'In order for trust to be restored to the Pennsylvania election system, Kathy Boockvar must resign as Secretary of State in Pennsylvania following these most recent efforts to weaken the state’s voting system and damage the integrity and confidence in our elections,' they continued.
Republicans are said to be keeping their legal options open to challenge absentee ballots in Pennsylvania, if the battleground state could swing President Donald Trump’s reelection.
Corman was reported in the Atlantic to have said that he and the state legislature would consider replacing the popular vote in Pennsylvania with Electoral College members of the legislature’s choosing if the voting result were too convoluted. He then reportedly distanced himself from the idea a short while later.
Experts told Yahoo News the election may now be heading towards what they call a 'nightmare scenario'.
While the majority of the country opted otherwise, Pennsylvania, Wisconsin and Michigan all resisted bipartisan entreaties to let their election clerks have their mail-in ballots counted by Election Day.
Consequently, each of the states will be counting absentee ballots for several days, with the count expected to last until Friday.
Philadelphia City Commissioner Al Schmidt told CNN: 'We are really running two election systems at the same time.'
He said there had been no break for people working on the ballots, but he said they had to flick from mail-in, to poll voters, back to mail-in.
He added: 'We are not stopping, we're going to continue. We have hundreds of people working. We're going to continue day and night.'
But when asked how long it would be before the results were in, Commissioner Schmidt said it will take all day Wednesday, Thursday and they have until Friday.
He added that some ballots had not arrived but would be counted if they were posted on time.
Just a few steps from the birthplace of the US, mail-in ballots are processed, flattened and scanned by poll workers in the Philadelphia Convention Center in Center City yesterday
'We may not know the results today, but I encourage all of us to take a deep breath and be patient,' Wolf said in his video as thousands of Pennsylvanias headed to the polls Tuesday to cast their ballots
Why have the crucial states taken so long to count votes? Pennsylvania is under fire for slow tally of mail-ins while Wisconsin is forced to fix misprinted ballots by hand because machine ran out of INK
Election officials in battleground states are facing mounting questions over bungled vote counting that left the result in limbo.
Slow tallying of absentee ballots, malfunctioning machines, ink shortages and printing errors that forced poll workers to count single ballot cards by hand in the early hours of Wednesday morning as America was kept waiting for the outcome.
The Midwestern states of Michigan, Wisconsin and Pennsylvania were all still up in the air as the sun rose on Wednesday, with officials caught flat-footed by the historic turnout that saw almost 100 million votes this year.
In all three states, officials were not allowed to begin counting ballots until on or just before election day. Republican-led state legislatures in the states had opposed changing laws to allow earlier preparations as other states did.
Pennsylvania, which may well be the deciding state in the election, will continue to accept ballots postmarked by Tuesday if they are received by 5pm on Friday.
The Keystone State holds 20 Electoral College votes and is one of the states considered the most critical for Trump to win reelection.
Wolf said in his video message: 'I believe the days ahead are our moment to shine, and we will do it as a state united as we count every vote.'
Trump lashed out against the Supreme Court ruling allowing Pennsylvania to accept absentee ballots received by Friday.
He said the results should be known on Tuesday night.
He said on a visit to his campaign headquarters in Arlington, Virginia: 'I think the ruling on Pennsylvania was an unfortunate one by the Supreme Court because I think we should know what happens on the night.
'Let people put their ballots in earlier,' he suggested of mail-in and absentee voting. 'But you have to have numbers, you can have these things delayed for many days and maybe weeks.
'You can't do that. The whole world is waiting, this country is waiting – but the whole world is waiting.'
'You have to have a date, and the date happens to be November 3,' the president reiterated. 'And we should be entitled to know who won on November 3.'
'They should put the ballot in earlier, there's no reason why they can't put the ballot in a few weeks earlier, one week earlier. I think it's a very dangerous decision for a country in many ways dangerous, in many ways.'
Gov Wolf tweeted after the comments: 'Let's be clear. This is a partisan attack on Pennsylvania's election, our votes and democracy.'
The Supreme Court also ruled last month North Carolina could continue accepting and counting mail-in ballots received eight days after Tuesday.
Although victors are not officially called on Election Day, projections by the media are usually accurate enough to predict the winner – and there is typically a concession and victory speech delivered the night of the election.
This year, however, everything is up-in-the-air.