Joe Biden flayed Donald Trump on Tuesday with accusations the US President has surrendered to a surging pandemic, as the Democrat took his campaign to the Republican stronghold of Georgia one week before the election.

While the former vice president went on electoral offense, seeking to expand the campaign map and his state-by-state path to victory on November 3, Trump barnstormed the Midwest in a last-gasp bid to shore up states that voted for him in 2016 but which polls show are tilting Biden's way.

And with the campaign narrowing down to its final days, Biden tapped one of his top surrogates, popular former president Barack Obama, to deliver a closing argument for Democrats in Florida, a must-win swing state for Trump if he is to defy the odds and earn reelection.

Biden, buoyed by poll numbers that show him leading the incumbent, drilled in on Trump's coronavirus response, reminding voters that Trump's chief of staff Mark Meadows conceded at the weekend that "we're not going to control the pandemic."

Speaking in Warm Springs, Georgia, Biden branded the response "a capitulation" by a White House that "never really tried" to halt a pandemic which has now killed more than 226,000 Americans.

Instead of acting as a wartime president to battle Covid-19 as he promised, Trump "shrugged, he swaggered and he surrendered," Biden said.

"I'm here to tell you: We can and we will control this virus," he added.

- 'Working my ass off!' -

Trump defeated Hillary Clinton by five points in Georgia in 2016, but polls have the 74-year-old running neck and neck with Biden in the Peach State.

Georgia last voted for a Democrat for president nearly three decades ago -- Bill Clinton in 1992 -- but the Biden campaign has high hopes of flipping the state, and also winning its two US Senate seats which are up for grabs.

Biden, 77, held a socially distanced drive-in rally later in Atlanta, Georgia's largest city, where he repeated some of the same attacks on Trump but also urged voters to recognize how vital the state suddenly is to winning the White House.

"We win Georgia, we win everything!" Biden said, his voice rising. "These are the final days, so keep that sense of empowerment with you, that sense of optimism."

Trump meanwhile maintained his hectic campaign pace, holding an open-air rally in Michigan followed by a similar one in Wisconsin and then Nebraska. Attendees did not practice social distancing, and many were maskless.

Michigan and Wisconsin are Midwestern battlegrounds which he won by razor-thin margins four years ago, but Trump insisted "we're leading almost everywhere" thanks to his frantic campaign schedule.

"I've got to say I'm working my ass off here!" he boomed in Lansing, Michigan, eliciting a huge cheer.

Trump also said his pandemic policies and economic chops would serve the nation better than Biden.

"This election is a choice between a Trump super-recovery or Biden depression," he said.

But with Covid-19 cases rising in several states and no agreement yet on a pandemic rescue package in Congress, US stocks mostly slid Tuesday for a third straight session.

Later in Wisconsin, Trump warned Americans that they should not "let this radical socialist group take over" with Biden as president.

"We didn't come this far and fight this hard to surrender our country back to the corrupt Washington swamp," he said at his final rally of the day in Omaha, Nebraska.

- 'Bring it home' -

Election tracking website RealClearPolitics has Biden up 7.4 points in an average of national polls -- a slight drop from just days ago. 

Trump dismissed the polls in a tweet Tuesday and accused the media of focusing on "Covid, Covid, Covid" to hurt his reelection chances.

With Biden maintaining a more constrained campaign schedule instead of hosting what he called Trump's "super-spreader" events, he dispatched Obama to Florida, where the race is on a knife-edge.

"One week until the most important election in our lifetimes," Obama told a crowd at a drive-in rally in Orlando. 

He delivered a searing indictment of Trump, accusing him of incompetence, repeated lies, embracing dictators and ignoring the pandemic.

But he also offered a blunt assessment of how apathy in 2016 may have cost Democrats the election and he urged them to make a plan and vote early.

"We were complacent last time. Folks got a little lazy, folks took things for granted, and look what happened," Obama said. 

"Not this time," he said. "Let's bring it home."

With Trump in the Midwest, First Lady Melania Trump hit the hustings for the first time this year.

"Donald is a fighter," she told Trump supporters in Pennsylvania, before turning to her husband's rabid Twitter use.

"I do not always agree with the way he says things," she said, to some laughter. "But it is important to him that he speaks directly to the people he serves."