Biden made his remarks in an interview with CBS on Sunday, his first since announcing in late July that he would withdraw from the race against Republican candidate Donald Trump over concerns about the future of US democracy.

Harris leads Trump by four points in Pennsylvania and two other key swing states, Wisconsin and Michigan, according to polls by the New York Times and Siena College released on Saturday.

Asked whether he would be campaigning for Harris, Biden replied: "Yes."

Biden said he and Pennsylvania Governor Josh Shapiro "are putting together a campaign tour in Pennsylvania. I'm going to be campaigning in other states as well, and I'm going to do whatever Kamala thinks I can do to help most."

Harris announced last week that Minnesota Governor Tim Walz would be her vice presidential running mate.

"He's my kind of guy, he's real, he's smart, I've known him for several decades. I think it's a hell of a team," said Biden.

The president, who decided to step down in the wake of a disastrous debate performance against Trump on June 27, said internal polls showed the race would have been very close.

"But what happened was, a number of my Democratic colleagues in the House and Senate thought that I was going to hurt them in the races and I was concerned if I stayed in the race, that would be the topic you'd be interviewing me about," he said.