President Donald Trump has cut Joe Biden's lead to nine points as the US election looms.

Joe Biden concentrated Tuesday's election campaigning on battleground states both see as critical to clinching an Electoral College victory, with the Democrat leading in the majority of swing states. 

Mr Biden went to Florida to court seniors, looking to deliver a knockout blow in a state Mr Trump needs to win while trying to woo a group whose support for the president has slipped.

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Trump visited Pennsylvania, arguably the most important state on the electoral map, unleashing fierce attacks on Mr Biden's fitness for office in his opponent's backyard.

Addressing a rally he said: "He's shot, folks. I hate to tell you, he's shot.

"Can you imagine if you lose to a guy like this? It's unbelievable."

In his second rally since contracting the coronavirus, Mr Trump spoke for more than an hour to a crowd of thousands packed in tightly and mostly maskless.

Touting his elimination of a federal rule that would have brought more low-income housing to the suburbs, he also zeroed in on groups whose support he has struggled to retain, including female voters turned off by his rhetoric.

"So I ask you to do me a favour. Suburban women: Will you please like me? Please. Please. I saved your damn neighbourhood, OK?" Mr Trump said.

"The other thing: I don't have that much time to be that nice. You know, I can do it, but I gotta go quickly."

Mr Biden spent the day in Florida, his third visit to the state in a month, looking to expand on his inroads with older voters.

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To the president, he said: "You're expendable, you're forgettable, you're virtually nobody," Mr Biden said at a senior centre in Pembroke Pines.

The "only senior Donald Trump seems to care about" is himself, Mr Biden added.

"I'm running as a proud Democrat, but I will govern as an American president," Mr Biden said to supporters blaring their horns as they listened from cars.

"I'll work as hard for those who vote against me as those who vote for me."