More than 47 million votes have already been cast for the November 3 US presidential election, eclipsing the total early voting from the 2016 election.

About 47.5 million Americans have turned in ballots, roughly eight times the number of early votes cast about same point before the 2016 presidential contest, according to data compiled by the US Elections Project.

The turnout eclipses the 47.2 million early votes that were cast before election day in 2016.

The surge comes after many states have expanded mail-in voting and in-person early voting as a safe way to vote during the coronavirus pandemic and amid voter eagerness to weigh in on the political future of Republican President Donald Trump, who is facing a stiff challenge from Democrat Joe Biden.

Mr Biden leads the President in national opinion polls, although surveys in crucial battleground states indicate a tighter race.

The high level of early voting has led Michael McDonald, the University of Florida professor who administers the US Elections Project, to predict a record turnout of about 150 million, representing 65 per cent of eligible voters, the highest rate since 1908.

Mr Trump has railed against mail-in voting, making unfounded accusations that it leads to fraud.

Experts have said such fraud is rare.

Those attacks by the President have shown signs of depressing Republican interest in voting by mail.

Democrats have roughly doubled the number of returned mail-in ballots by Republicans in states that report voter registration data by party, according to the Elections Project.

Debate mute button

The early voting data comes as Mr Trump and Mr Biden meet in the second US Election debate.

The first debate was a confrontational affair with both candidates regularly interrupting and talking over each other.

The second debate will include a representative of the Commission on Presidential Debates manning a mute button to ensure each candidate has two full minutes uninterrupted to deliver opening answers to six major topics, according to debate commission chair Frank Fahrenkopf.

A member of the Trump and Biden campaigns is expected to monitor the person who controls the mute button backstage, Mr Fahrenkopf said, noting the button would not be used beyond the first four minutes of each topic.

The mute button is among a handful of changes implemented by the nonpartisan debate commission to help ensure a better sense of safety and order following the raucous opening debate 23 days ago. Trump was diagnosed with COVID-19 two days after that first meeting.

Mr Trump and Mr Biden will be separated on stage by plexiglass barriers – despite objections from the Trump campaign.

Additionally, any audience member who refuses to wear a mask will be removed, organisers report. Last month, several members of the Trump family removed their masks once seated in the debate hall.

-with agencies