Donald Trump has fuelled the controversy over claims that Joe Biden’s running-mate Kamala Harris was not born in the United States.

Harris, who was unveiled this week, was born in Oakland, California to an Indian mother and Jamaican father on October 20, 1964.

But Trump, who ploughed an unfounded ‘birther’ theory about former president Barack Obama during his 2016 US election campaign, refused to rule out the validity of claims that Harris was not born in America.

He said: "I just heard it today that she doesn't meet the requirements and by the way the lawyer that wrote that piece is a very highly qualified, very talented lawyer.

"I have no idea if that's right. I would have assumed the Democrats would have checked that out before she gets chosen to run for vice-president.

"But that's a very serious, you're saying that, they're saying that she doesn't qualify because she wasn't born in this country."

Trump was refrencing Tim Fitton, the head of conservative group Judicial Watch, who tweeted speculation about Harris being 'ineligible to be vice-president under the US constitution's citizenship clause’.

The post was subsequently retweeted by one of Trump’s campaign advisers, Jenna Ellis.

But the claims were immediately rubbished by Northwestern University law professor Juliet Sorensen.

She told the Associated Press news agency: "The VP has the same eligibility requirements as the president.

"Kamala Harris, she has to be a natural-born citizen, at least 35 years old, and a resident in the United States for at least 14 years. She is. That's really the end of the inquiry."

Trump and Biden will go head-to-head in the US presidential election on November 3.