US President Donald Trump and Democratic challenger Joe Biden waged pitched battles for the American Midwest today, chasing every last vote with four days to go in a region that propelled the Republican to victory in 2016.

The pair are each barnstorming three heartland states, with a resurgent coronavirus passing the alarming milestone of nine million cases as they hit the stump - highlighting their differences in a race overshadowed by the pandemic.

Mr Trump, heralding a "big day" of campaigning as he left the White House, held a rally in Michigan before heading to Green Bay Austin Straubel International Airport in Green Bay, Wisconsin - his next stop will be Minnesota.

"We just want normal," he told supporters earlier today - many of them unmasked - at an outdoor "Make America Great Again" rally near Detroit as he pushed states to relax public health restrictions and resume daily life.

Supporters awaiting the arrival of Donald Trump at Rochester airport, Minnesota

He again bucked his own administration's health experts as he downplayed the Covid-19 threat, saying "if you get it, you're going to get better, and then you're going to be immune."

Covid-19 has killed 230,000 people in the US and the outbreak has ravaged the economy. While there have been signs of recovery, millions remain jobless.

Joe Biden was also stumping in Wisconsin and Minnesota, after the Democrat's first stop of the day in Iowa, where he flayed Trump over his handling of the pandemic.

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"Donald Trump has given up (and) waved the white flag," Mr Biden told a drive-in rally with more than 300 cars in Des Moines.

Mr Biden, tailoring his speech to the Iowa crowd, also bashed the president for saying America's farmers were "doing better now than when they had a farm," after Mr Trump's administration began paying billions of dollars in federal subsidies to farmers amid a trade war with China.

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

It is Mr 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.

A Democratic voter at Joe Biden's drive-in rally in Iowa

So can Biden win over enough voters to prevail in the Hawkeye State? "I wouldn't put money on it," Iowa attorney Sara Riley, 61, said at the drive-in rally, although she was more confident about him clinching the White House.

"I think Americans, even Trump supporters, want to get to a place where the country is less divided," Ms Riley said.

With voters concerned about the health hazards of crowded polling stations on 3 November, a record 85 million have already cast early ballots by mail or in person.

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

The state reported that a staggering nine million residents had already voted, surpassing its entire 2016 total.

Mr Biden's running mate Kamala Harris visited Texas today in a bid to turn the state Democratic for the first time since president Jimmy Carter in 1976.

Kamala Harris speaking at Fort Worth, Texas today

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

Mr Biden winning there would be a dagger to Mr Trump, but the president dismissed the notion as he left the White house, saying: "Texas, we're doing very well."

Mr Trump and Mr Biden are focusing their greatest efforts on traditional battlegrounds that will decide the election - such as Florida, where both campaigned on Thursday.

Mr Biden argued in Tampa that he would bring responsible leadership after months of the White House downplaying the virus.

"I'm not going to shut down the economy, I'm not going to shut down the country. I'm going to shut down the virus," he said.

Tomorrow, the Democratic hopeful returns to the Midwest bringing with him perhaps his strongest surrogate: ex-president Barack Obama, making his first joint in-person campaign appearance of the year with his former VP.

Mr Trump will spend tomorrow campaigning in the critical state of Pennsylvania, where he narrowly trails Mr Biden in polls.