With eight days until the US election, US President Donald Trump is wooing voters in Pennsylvania, a state he won in 2016 and is crucial to his chances of fending off Democratic challenger Joe Biden and winning a second term.

“We win Pennsylvania, we win the whole thing,” the Republican President told cheering supporters in Allentown, predicting victory in a state where opinion polls indicate he is trailing Mr Biden.

More than 60 million people have already cast ballots ahead of the November 3 election in a record-breaking pace that could lead to the highest US voter turnout by percentage in more than a century.

Surging coronavirus cases in many parts of the country and a COVID-19 outbreak within Vice President Mike Pence’s staff have kept the focus of the race on the pandemic.

Mr Pence campaigned in Minnesota on Tuesday (Australian time) after an appearance in North Carolina on Sunday. He tested negative for the coronavirus on Monday, his office said, after multiple senior aides tested positive over the weekend.

Despite Mr Biden’s solid lead in US opinion polls, the contest appears tighter in the most critical battleground states that could decide the outcome.

A state where voters can swing toward either major party, Pennsylvania has been heavily courted with frequent visits by both candidates.

Mr Trump was due to speak later in the day in Lititz and Martinsburg.

Mr Trump also planned multiple stops in Michigan and Wisconsin this week as well as visits to Arizona, Nebraska and Nevada.

Mr Biden, born in Pennsylvania, has made a victory in the state a critical part of his own strategy.

Mr Trump said he expected to win Pennsylvania by a larger margin than the narrow one he achieved in defeating Democrat Hillary Clinton in 2016.

Tweet from @AndrewPollackFL

Addressing supporters, Mr Trump touched on what he called “an existential” issue for Pennsylvania, Mr Biden’s comment during last week’s presidential debate that if elected he would “transition” the US away from oil and natural gas.

“He wants to go with windmills that are made in Germany and China,” Mr Trump said, adding “Biden’s plan is an economic death sentence for Pennsylvania’s energy sector”.

Mr Biden was expected to remain in his home state of Delaware on Tuesday (Australian time).

He is scheduled to travel to Georgia on Tuesday, with stops in Atlanta and Warm Springs, and Florida on Thursday, with stops in Broward County and Tampa.

Mr Biden will be aided in Florida with an appearance in Orlando on Wednesday (Australian time) by former president Barack Obama.

-AAP