Former US President Barack Obama and his wife Michelle endorsed Kamala Harris' bid for president on Friday in a roughly one-minute long video that captured a private phone call between the couple and the current vice president.

"We called to say Michelle and I couldn't be prouder to endorse you and to do everything we can to get you through this election and into the Oval Office," Obama told Harris.

"I am proud of you. This is going to be historic," the former first lady told Harris.