Donald Trump has called for drug tests to be conducted on him and Joe Biden ahead of their first presidential election debate.

The President will come face-to-face with the Democratic nominee for the first time on September 29.

And in a bizarre rant, Trump believes drug tests need to be carried out because of the way he feels Biden has improved in debates since he first began his campaign.

Speaking to the Washington Examiner, he said: "I don't know how he could have been so incompetent in his debate performances and then all of a sudden be OK against Bernie.

"My point is, if you go back and watch some of those numerous debates, he was so bad.

"He wasn't even coherent. And against Bernie, he was. And we're calling for a drug test."

Trump called for a drug test to be conducted on himself and Hillary Clinton four years ago before 2016 election.

Neither he nor Clinton ended up being tested.

The president then referred to the debate as a ‘prizefight’ and likened himself and Biden to gladiators.

He added: "It's no different from the gladiators, except we have to use our brain and our mouth. And our body to stand. I want all standing, they want to sit down."

Biden is currently eight points ahead in the election polls with less than 11 weeks until Americans head to the ballot.