U.S. President Joe Biden on Saturday (October 25) encouraged voters to follow their "gut" when casting their ballots in the upcoming November 5th presidential election, which he describes as "the most important election of our lifetime.''

Biden spoke at a 'Get out the vote' event in Pittsburgh where he arrived to support Democratic presidential candidate Kamala Harris who he said "has a backbone like a ramrod".

Rounding on former U.S. President Donald Trump, Biden described the Republican nominee as a ''loser.''

Harris is leading her opponent Trump nationally by a marginal 46 percent to 43 percent, a recent Reuters/Ipsos poll showed.

During his speech Biden mentioned the vocal Trump supporting billionaire Elon Musk, referring to him as the world's wealthiest man who "turned out to be a illegal worker", upon his arrival to the United States on student visa.

READ: The Obamas stump for Harris, key allies in final days of campaign

Musk has given about $44 million to his pro-Donald Trump spending group during the first half of October, federal disclosures showed on Thursday.

The contributions, disclosed in a filing to the Federal Election Commission by Musk's America PAC group, come after a prior report showed he gave the group around $75 million over three months between July and September.

As part of its plan to stir support for Trump, America PAC has been giving away $1 million per day to a randomly selected signatory of its online petition, which is only open to registered voters in battleground states.

(Production: Maria Vasilyeva)