President Donald Trump and challenger Joe Biden took their White House battle to the American Midwest on Friday, chasing every last vote with four days to go in a region that propelled the Republican to victory in 2016.

Trump and Biden are each barnstorming three heartland states, as a resurgent coronavirus highlights their differences in a race overshadowed by the pandemic, which has cost 228,000 lives.

"It will be a big day," Trump told reporters as he left the White House for Michigan, before heading on to Wisconsin and Minnesota where he will converge with the Democrat Biden — who makes his first stop of the day in Iowa.

Trump flipped Iowa, Michigan and Wisconsin from the Democrats to clinch his shock victory four years ago. Now Biden is aiming to snatch them back, and polls show him leading in all three, albeit narrowly in Iowa.

"I don’t take anything for granted,” Biden — who is ramping up his ground game in the closing days of the race — said before departing his hometown of Wilmington, Delaware.

"We’re going to work for every single vote up ‘til the last minute.”

It is Biden’s first time in Iowa since his inauspicious campaign start in February, when he finished a dismal fourth in the opening Democratic nominating contest.

The Democrat is also seeking to counter Trump in Minnesota, where the president has invested heavily — reiterating Friday he was intent on flipping the state.

With voters concerned about the health hazards of crowded polling stations on November 3, a record 84 million Americans have already cast early ballots by mail or in person.

Even as the United States hit a grim new record in daily COVID-19 infections Trump is sticking to his guns, downplaying the virus’ dangers and branding Democrats as rampaging "socialists” intent on shutting the country down.

Biden has sought to persuade the few remaining undecided voters that he would provide a steady hand on the wheel and heal America’s "soul”, calling Trump irresponsible.

The 77-year-old former vice president has held drive-in, socially distanced rallies, while Trump’s large outdoor gatherings — such as a raucous affair Thursday in Tampa, Florida — have often been shoulder-to-shoulder, and largely mask-free.

After a campaign largely muted by the pandemic, Biden in the final stretch is on the offensive, pushing Trump onto the back foot in unexpected battlegrounds like Texas, a large, traditionally conservative bastion now rated a tossup by multiple analysts.

On Friday the state reported that a staggering nine million of its residents have already voted, surpassing its entire vote total in the 2016 election.

Biden’s running mate Kamala Harris was set to visit Texas making 11th-hour appeals to voters in a bid to turn the state Democratic for the first time since Jimmy Carter in 1976.

"We have a chance to turn Texas blue,” the 96-year-old Carter said in a fundraising email Friday.

But Trump dismissed the notion as he left the White house, saying: "Texas we’re doing very well.”

Both Trump and Biden are focusing their greatest efforts on traditional battlegrounds that will decide the election — such as Florida where both travelled on Thursday