Kamala Harris entered the election race unexpectedly after US President Joe Biden dropped out in July
Kamala Harris entered the election race unexpectedly after US President Joe Biden dropped out in July AFP

US presidential candidates Donald Trump and Kamala Harris head to key battleground states on Friday, each seeking an edge in a race where they are running neck-and-neck less than two months before voting day.

Trump, 78, heads to Nevada, where his campaign says he will focus on delivering a message on the economy -- a key issue in this election, with US inflation slowing but still higher than most consumers are used to.

Harris, 59, will be in perhaps the most crucial swing state, Pennsylvania, where earlier this week she debated Trump for the first time, landing several barbs that appeared to get under the Republican's skin.

Voters will head to the polls on November 5, with both candidates in a dead heat according to most polls, including in the battleground states likely to decide the election under the United States' electoral college system.

Republican Trump, always an aggressive speaker, has turned up the heat on his rhetoric as Harris has closed the gap in recent weeks, taking aim at her with pointed insults and claiming there is an ongoing "invasion" of migrants into the United States.

At a rally in Arizona on Thursday, Trump called Harris a "lunatic" and accused the moderators of the debate earlier in the week of being biased against him.

He also ruled out participating in another debate with the Democratic vice president.

Hammering away at the key election issue of immigration, Trump repeated unfounded allegations against Haitian migrants in the Ohio town of Springfield, claiming they were eating residents' pets.

If elected, the Republican candidate promised to fight illegal immigration with mass deportations, which drew chants of "USA! USA!" from his audience.

In recent days, Trump has frequently been seen with Laura Loomer, a radical right-wing activist who has been known to peddle unfounded conspiracy theories, including regarding the 9/11 terror attacks on the United States.

She has hit out at Harris, whose mother is Indian, recently saying that in the event of the Democrat's victory, the White House would "smell like curry."

Harris has, so far, not responded to her rival's personal attacks.

When Trump brought up the false story about pets being eaten by migrants in their televised debate on Tuesday, she responded by shaking her head disbelievingly.

On Thursday, Harris delivered her well-honed stump speech in North Carolina, another key battleground in the election.

"It's time to turn the page" on Trump, she said, promising to defend the US middle class and women's reproductive rights.

Harris entered the race unexpectedly after US President Joe Biden dropped out in July, following a disastrous performance in a televised debate against Trump.

On Thursday, she insisted that she remained "the underdog" in the race.

"We know ours will be a very tight race until the very end. We are the underdog. Let's be clear about that," she said.

In a race that is neck-and-neck, the election is likely to come down to a few tens of thousands of undecided voters in battleground states.

Donald Trump has ruled out participating in another presidential debate with Vice President Kamala Harris
Donald Trump has ruled out participating in another presidential debate with Vice President Kamala Harris AFP