PITTSBURGH, United States (AFP)— Kamala Harris and Donald Trump launched a final frenzied campaign blitz Monday, hitting must-win Pennsylvania on the last day of a volatile US presidential race that polls say is hurtling towards a photo finish.

At his first rally of the day in North Carolina, Trump, 78, shrugged off accusations that his age and the gruelling election schedule had left him physically and mentally exhausted.

“I don’t even sleep. I’ve gone through 62 days without a day off,” he said in an insult-laden 90-minute stump speech that he has delivered dozens of times in recent weeks.

Harris said she was “feeling good” and gave a thumbs-up as she boarded her plane to her first event of the day in Allentown, Pennsylvania.

Republican Trump has promised a “landslide” as he seeks a sensational return to the White House, while Democrat Harris said “momentum” was on the side of her bid to be America’s first woman president.

But the polls suggest a deadlock nationally, and also in the seven swing states where the winner is expected to be decided.

The world is anxiously watching as the outcome is set to have major implications for conflicts in the Middle East and Russia’s war in Ukraine, and for tackling climate change, which Trump has called a hoax.

US democracy could also be tested as Trump is expected to reject the result if he loses, raising the prospect of political chaos, civil unrest and violence.

“Donald Trump and his campaign are already telegraphing they may declare victory prematurely. We fully expect him to,” Harris spokesman Ian Sams said Monday.

“It’s a sign of weakness and concern he may lose, to sow doubt in the nonpartisan election officials.”

After many dramatic twists, including two bids to kill Trump and Harris’s shock late entrance, the race is coming down to Pennsylvania, the most fought-over battleground state.

Trump and Harris will hold duelling rallies in the industrial city of Pittsburgh, highlighting how Pennsylvania is the single biggest swing state prize under the US Electoral College system, which awards influence in line with population.

Harris will spend the whole day campaigning in the state, culminating in a rally in Philadelphia featuring singer Lady Gaga. Trump will travel from North Carolina on to Pennsylvania and then Michigan.

Both sides say they are encouraged by early turnout, with over 78 million people having voted already, around half of the total number of ballots cast in 2020.

The closeness of the 2024 White House race reflects a divided United States, as it chooses between two candidates whose visions could scarcely be more different.