Donald Trump, challenger Joe Biden and their top surrogates were barreling through crucial states in the industrial Midwest and the coastal southeast on Saturday, in a frantic sprint to mobilize voters as they pressed their closing arguments with the US presidential election only days away.

Using some of his most urgent language yet, Trump warned of "bedlam in our country" if no clear winner emerges quickly in the November 3 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 meantime told backers it was "time for Donald Trump to pack his bags and go home."

Underscoring the high stakes -- and the disruptive impact of the coronavirus pandemic -- 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 nearly 230,000 Americans, ravaged the world's largest economy and was infecting record numbers of people across the US.

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

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

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

Pennsylvania has emerged as one of the top prizes this year. 

In his motorcade en route to rural Bucks County, the president passed hundreds of supporters holding up a forest of pro-Trump signs. The crowd then booed reporters in trailing vehicles.

In remarks at an event there, Trump lashed out at Biden, saying he would shut down the state's fossil-fuel industry.

The president claimed credit for creating the "greatest economy in the history of this country -- the history of the world" -- while "foreign nations are in freefall."

Despite recent signs of recovery, however, millions remain jobless.

And the race has been overshadowed by the surging pandemic, which had even sickened Trump and many members of his staff. 

More than 94,000 new infections were recorded Friday in the US -- another new high -- and total cases passed nine million, according to data from Johns Hopkins University.

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.

After Biden and Obama appeared Saturday before a socially distanced drive-in rally in Flint, they made an unannounced stop in suburban Bloomfield Hills before heading later to Detroit to be joined by superstar singer Stevie Wonder. 

Biden leads in the state by nearly seven points, according to a RealClearPolitics average of polls. The state's 16 electoral votes could provide a sizable leap towards the 270 needed to win the White House. 

Trump, in eking out his 2016 victory, took advantage of low turnout rates among Michigan Blacks. As Biden campaigns with the nation's first Black president, he clearly hopes to change that.

Obama pulled few punches in Flint, saying 140,000 American lives would have been saved if the president had taken an approach to the pandemic similar to Canada's. Trump, he added, was on course to be the first president in nearly a century to preside over a net job loss.

Biden then took the stage to tear into Trump.  

"We're done with the chaos, the tweets, the anger, the failure, the refusal to take any responsibility," he said.

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 their windows, and police are preparing for the possibility of violence.

Biden's campaign announced he will address the nation on election night, after a vote that will undoubtedly leave millions bitterly disappointed, no matter who wins.

 - Chasing every vote -

 On Friday the two candidates carried their battle to the American Midwest, barnstorming three heartland states each as they chased every last vote.

Trump, who has long said the virus will "disappear," remained defiant at rallies in Michigan, Wisconsin and Minnesota. 

He again downplayed the threat of the coronavirus, saying, "If you get it, you're going to get better, and then you're going to be immune."

After a campaign largely muted by the pandemic, Biden has taken the offensive, pushing Trump onto the back foot in unexpected battlegrounds like Texas, a large, traditionally conservative bastion now seen as a toss-up.

On Friday, the state reported that a staggering nine million residents had already voted, surpassing its 2016 total.

Harris visited Texas Friday in a bid to turn the state Democratic for the first time since 1976.