Kalamazoo, Michigan - In their search for holdout votes 10 days before the US election, Kamala Harris was to be joined on the campaign trail Saturday by Michelle Obama while Donald Trump targeted migrants at a raucous rally.

The two rivals for the White House converged on Michigan, one of the three "Blue Wall" states – along with Wisconsin and Pennsylvania – that could be critical to victory on November 5.

At his rally, Trump launched bitter personal attacks on Harris and falsely accused her of pushing an "open border" migration policy.

"She's a dope," he said. "This person cannot be president."

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"She will destroy our country. Everyone knows it. No one respects her.

"The United States is now occupied country. Kamala broke it, we will fix it."

Fresh off a rally in Texas with pop icon Beyoncé, Harris was deploying one of the most popular figures in US politics: former first lady Michelle Obama, for a rally later Saturday in Kalamazoo, Michigan.

After flying from Houston, Harris kept her focus on abortion rights – a weak point for Republicans – by visiting a local doctor's office and meeting with physicians, staff, and medical students.

"Because of Trump and what he did with the Supreme Court, we are looking at a health care crisis in America," Harris told reporters, referring to justices chosen by Trump who tipped the court into ending the national right to abortion in 2022.

Election polls forecast a virtual dead heat, and with more than 38 million people already casting early ballots, Americans are deciding whether to elect the country's first-ever woman president, or its oldest commander in chief.

Trump still refuses to accept his defeat in the vote four years ago and is expected to reject the result if he loses again – potentially pitching the US into chaos.

Harris (60) campaigns Sunday in Philadelphia, Pennsylvania, the largest city in the largest of the swing states likely to determine the winner under the US electoral college system.

She will crisscross the city trying to persuade residents to cast their ballot, especially in historically Black and Latino districts.

Trump, who swept the three Blue Wall states in his shock victory in 2016 only to see Joe Biden reclaim them four years later, hopes to claw back one or more of the trio and win the so-called Sun Belt swing states to propel him back into the White House.

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With just a few thousand votes possibly the difference between victory and defeat in the tightest of swing states, Trump will already be in Pennsylvania for a rally later Saturday.

While Harris appeared alongside Beyoncé on Friday evening, Trump had a three-hour interview with Joe Rogan, America's most popular podcaster.

On Sunday night, Trump will rally his supporters in Madison Square Garden, the iconic arena in the heart of heavily Democratic New York.

The brash billionaire and onetime reality television star may be keen to orchestrate a spectacle, and demonstrate he can fill an arena in a liberal bastion.

But critics, including Trump's 2016 rival Hillary Clinton, have noted that Madison Square Garden was also the scene of a 1939 pro-Nazi rally organized by a group supportive of Adolf Hitler.

Part of Harris's election strategy is to peel moderate Republicans away from Trump, who often demeans some Americans as the "enemy."