More than 95 million Americans had cast their votes in the 2020 presidential election by Monday, according to a tally by the US Elections Project at the University of Florida, a harbinger of what is expected to be the highest turnout of modern times.

Just a day before Election Day, the record-breaking number is equal to 69 per cent of the entire voter turnout for the 2016 election.

A sharp increase in mail-in and early in-person voting was largely prompted by the coronavirus pandemic, which has killed more than 230,000 people in the United States and continues unabated in many US states.

Read: Counting the vote in US: Will we know who won on election night?

President Donald Trump, his administration criticised for its handling of the Covid-19 outbreak, trails Democratic challenger Joe Biden in national opinion polls. A Reuters/Ipsos poll taken on October 27-29 shows Biden ahead, 51pc to 43pc.

But the race is still a toss-up in battleground states that decide the election through the Electoral College, including Arizona, Florida and North Carolina.

A large number of Trump's Republican supporters are expected to turn up in person to vote on Election Day after Trump sowed distrust, without evidence, of mail-in voting by asserting it was riddled with fraud.

Democrats have largely embraced early voting, not only because of the pandemic, but also because of steps the Trump administration has taken to slow down the processing of US mail.

Experts predict turnout will easily surpass the 138 million who voted in 2016. Only 47 million votes were submitted before Election Day four years ago.