President Donald Trump and challenger Joe Biden were set to rally voters just hours apart in the Florida city of Tampa yesterday, their campaign paths crossing for the first time as the rivals' fight for the White House enters its frenetic final days. 

Florida, with 29 electoral votes, is a must-win prize, and polls show the candidates in a dead heat in America's third-largest state, which has sided with the winner in every presidential election since 1964, with one exception.

The candidates' events are sure to be a study in contrasts, with Trump's largely mask-less and densely packed supporters gathering in the afternoon, and Biden holding a socially distanced drive-in meeting later in the evening.

A day prior, Trump was stumping in Arizona, while Biden voted in his home state of Delaware and met with health experts, as he fine-tuned his pandemic response plan, seeking to reassure voters that he would use science to fight the contagion.

The virus has killed more than 227,000 people in the US and forced millions out of work in the world's largest economy as a resurgent wave of cases was reaching record levels.

"I'm not running on a false promise of being able to end this pandemic by flipping a switch," said the 77-year-old former vice president, who has a strong lead in opinion polls.

"But what I can promise you is this: We'll start on Day 1 by doing the right thing. We'll let science guide our decisions."

Tomorrow, Biden is to get some star power when he is joined on the stump in Michigan by Barack Obama, whom he served as vice president. It will be their first joint in-person appearance of the 2020 race, though Obama has been delivering strategically timed broadsides at Trump throughout.

Trump, by contrast, is finishing his campaign in an extreme test of endurance, with a final attempt to catch up both in swing states and also states that he won in 2016 but now has to defend.

After rallying supporters in three states Tuesday, Trump, 74, overnighted in a fourth -- Nevada -- and then flew to Arizona for two more rallies.

On an airport tarmac in Bullhead City, Arizona, Trump all but ignored the Covid-19 crisis, and many supporters did not bother with masks as they cheered his defiant insistence on a landslide victory November 3.

"It's going to be a great, great red wave," he boomed, referring to the Republican color. "We love you! We love you!" the enthusiastic crowd chanted back.

At another rally, in Goodyear, Arizona, Trump predicted he'd repeat his 2016 upset, saying: "We're going to have an even bigger surprise in six days."

The pandemic has upended all aspects of American life and overshadowed the election, with polls showing it may well be the president's undoing as cases hit record levels in the US.

More than 76.5 million people have cast early in-person and mail ballots nationally, according to data compiled by the US Elections Project at the University of Florida. That is a record-setting pace and more than 53% of the total 2016 turnout.

Some 57.4 percent of Americans disapprove of Trump's coronavirus response, while 39.8 percent approve, according to a poll average compiled by tracker FiveThirtyEight.com.

Biden has seized on that to build an impressive advantage in polls heading into the final week and is looking to expand his state-by-state path to victory.

On Tuesday, Biden visited Georgia, traditionally Republican territory, and he has said he will travel to Florida, Wisconsin and Michigan in the race's closing days.

All are states that Trump won in 2016 but that are up for grabs this year.

On Wednesday, Trump kept up his scorn for Biden's focus on health safety, saying that the Democrat would destroy the country through more lockdowns.

"If you vote for Biden, it means no kids in school, no graduation, no Christmas and no Fourth of July together. Other than that, you'll have a wonderful life."

Trump plans to return to the Midwest today, campaigning in Michigan, Wisconsin and Minnesota. In all, he plans to visit 10 states in the last week of the campaign and will host 11 rallies in the final 48 hours, a campaign official said.