President Donald Trump and Democratic Party nominee Joe Biden face off in the final presidential debate in Nashville, Tennessee. Photo: VCG

Donald Trump, challenger Joe Biden and their top surrogates barreled through crucial states in the industrial Midwest and coastal southeast on ­Saturday, ­pressing closing arguments in a frantic sprint days ahead of the US presidential election.

Using some of his most urgent language yet, Trump warned of "bedlam in our country" if no clear winner emerges quickly in Tuesday's election, saying, without evidence, that it could take weeks to sort out a result and that "very bad things" could happen in the interim.

Biden meanwhile told backers it was "time for Donald Trump to pack his bags and go home."

Underscoring the high stakes, a record 90 million early votes have already been cast, as the bruising contest heads toward the biggest turnout in at least a century. 

The virus has killed over 230,000 Americans, ravaged the world's largest economy and is infecting record numbers of people across the US.

The election takes place in a deeply divided country, with feelings so raw that gun sales have surged in some areas. Businesses in some cities, including Washington, are protectively boarding windows, and police are preparing for the possibility of violence.

Trump was focusing Saturday on the key battleground state of Pennsylvania - "the state where the story of American independence began," he said in Newtown, the first of four stops in that state amid a frenetic final sprint.

Biden made his first joint appearance of the campaign with Barack Obama in Michigan, as they scramble to boost turnout in a state Trump carried by a razor-thin margin in 2016. 

Vice President Mike Pence was meanwhile campaigning in narrowly divided North Carolina as Biden's running mate Kamala Harris was in Florida, another vitally important swing state.

Pennsylvania has emerged as one of the top prizes in 2020. The president's campaign has been overshadowed by the surging pandemic, which even sickened Trump and members of his staff. 

In stark contrast to Trump, who has belittled mask-wearing by Biden and others, the Democrat has scrupulously followed the guidance of public health experts.