Pennsylvania Governor calls for patience before polls close

"Across the state, dedicated county workers are ready to tirelessly make sure everyone's vote counts," CNN quoted Wolf as saying in a video message.

"But counting that tremendous number of ballots will take more time than we are used to. We may not know the results today, but I encourage all of us to take a deep breath and be patient.

"What is most important is that we have accurate results, even if that takes a little longer," he added.

In Pennsylvania, where the two candidates spent the weekend campaigning in a last-ditch efforts to garner votes, an NBC News-Marist poll released on Monday placed Biden ahead with a 5-point lead, 51 per cent to 46 per cent.

Meanwhile, the RealClearPolitics polling average gave the former Vice President a 4.3 percentage point lead over the President.

But the state's results won't be immediately due to the large number of early and mail-in votes that have already been cast.

Besides the Trump-Biden race, all 435 seats in the US House of Representatives and 35 of the 100 seats in the Senate were also be in the fray on Tuesday.

More than a dozen state and territorial governorships, among many other state and local posts, will also be contested.