Former US president George H W Bush plans to vote for Hillary Clinton in an unprecedented snub of the Republican candidate, Donald Trump, according to a member of the Kennedy family.

Kathleen Hartington Kennedy Townsend, the daughter of the late Robert F Kennedy, posted a picture on her Facebook page in which she is shaking hands with Mr Bush, with the caption: "The President told me he’s voting for Hillary!!”

She confirmed to Politico that the Republican grandee, who served as president from 1989 to 1993 and vice president from 1981 to 1989, would be voting for the Democrat candidate for the White House.

“That’s what he said,” she told the news website.