Kamala Harris turned 60 on Sunday in the final stretch of a knife-edge US election, making campaign stops at Black churches in Georgia as her 78-year-old opponent Donald Trump served fries at a Pennsylvania McDonald's in a bid to earn working-class credibility.

Kamala Harris questioned Donald Trump's fitness for office Friday as the oldest major-party White House candidate in history faced speculation that he is "exhausted" after backing out of a spate of interviews.

Kamala Harris rallied supporters in the swing state of Wisconsin on Thursday while Donald Trump stirred controversy with criticism of embattled ally Ukraine, as the rivals vied for the remaining undecided voters in a deadlocked US presidential election.