Democrat presidential candidate Kamala Harris has appeared on Saturday Night Live, as a surprise poll found she had “leaped” Donald Trump in a state thought to be in the bag for Republicans.

The respected Selzer poll for the Des Moines Register showed Harris leading 47 per cent to Trump’s 44 per cent in Iowa, reversing Trump’s four-point lead in September and his 18-point lead in June.

Iowa was largely considered the former president’s stronghold after he won the state in the past two presidential elections.

The startling poll, from a pollster with a track record, has shaken up the contest again just days out from the seemingly deadlocked US election on Tuesday (US time).

“It’s hard for anybody to say they saw this coming,” pollster J. Ann Selzer told the Des Moines Register. “She (Harris) has clearly leaped into a leading position.”

The results showed that women, especially older women, were driving the late shift towards Vice President Harris.

Nationwide opinion polls show the pair locked in a tight race, with Harris bolstered by strong support among women voters while Trump gains ground with Hispanic voters, particularly men.

Trump dismissed the Iowa poll as fake news, saying his own figures showed him winning Iowa.

“I got a poll, I’m 10 points up in Iowa. One of my enemies puts out a poll, I’m three down. They just announced a fake poll,” he said.

“Think of it, right before the election that I’m three points down. I’m not down in Iowa.”

Trump also appeared to be laying the groundwork to dispute the outcome of the election if he loses, re-using a sinister trick from his 2020 playbook.

At a weekend rally in Pennsylvania, Trump repeatedly criticised the US election process and voting machines, and called his opponents cheaters.

“They are fighting so hard to steal this damn thing,” Trump said.

“We got a bunch of cheaters that all they do is think about how they can cheat.”

Meanwhile, Harris made a surprise appearance on Saturday Night Live, portraying herself opposite the actor who plays her on the show, Maya Rudolph.

Dressed identically in a black suit and pearls, the two traded variations on Harris’s first name, saying Americans wanted to “end the drama-la” in politics “with a cool new step-mom-ala”.

“Keep Calm-ala and carry on-ala,” they said in unison.

“I don’t really laugh like that, do I?” Harris asked, after Rudolph imitated her distinctive chortle.

“A little bit,” Rudolph responded.

It was Harris’s first time on the  show, which has had other presidential candidates over its decades-long run.

“It was fun,” she told reporters on the tarmac before flying to Detroit in the battleground state of Michigan.

Trump appeared during his first presidential bid in 2015 when he poked fun at his tendency to exaggerate and steer clear of policy specifics.

He also appeared in 2004, long before he entered politics.

A Trump aide said he did not know if he had been invited to appear this year.

Earlier on Saturday (US time), Harris and Trump’s planes shared the tarmac in Charlotte, North Carolina, as the two candidates held duelling events in the southern state — one of a handful that will determine the outcome of Tuesday’s election (Wednesday Australian time).

It was the fourth day in a row that the candidates campaigned in the same state.

Trump and Harris stuck to familiar themes during their appearances.

Trump said he would deport millions of immigrants if elected and warned that if Harris won, “every town in America would be turned into a squalid, dangerous refugee camp”.

Campaigning in Atlanta, Harris said Trump would abuse his power if he returned to the White House.

“This is someone who is increasingly unstable, obsessed with revenge, consumed with grievance, and the man is out for unchecked power,” she said.

Republican presidential candidate Donald Trump rallies in Lititz, Pennsylvania. Photo: AAP

More than 75 million Americans have already cast ballots, according to the Election Lab at the University of Florida, in a sign of voter enthusiasm.

In North Carolina, the western counties that were devastated by Hurricane Helene appeared to be voting at roughly the same rate as the rest of the state, according to Catawba College political science professor Michael Bitzer.

At a later rally in Salem, Virginia, Trump said he ran for office to rescue the economy from “obliteration” even though it would have been easier to relax at one of his oceanfront resorts.

“I didn’t need to be here today,” he said.

“I could have been standing on that beach, my beautiful white skin getting nice and being smacked, being smacked in the face by a wave loaded up with salt water.”

Trump was joined on stage by women from a local college swim team who have objected to competing against transgender athletes.

Some of Trump’s TV ads have sought to capitalise on transgender controversies.

-with AAP