Aurora, Colorado - Donald Trump painted an apocalyptic picture of a country being "occupied" by hordes of criminal foreigners in a campaign speech Friday as he escalated his efforts to make November's US election about a migrant crime wave that isn't happening.

With the White House race neck-and-neck in the final stretch, the Republican ex-president has been dividing his closing pitch between a protectionist economic message and riling his largely white, working-class supporters by demonizing immigrants.

As his Democratic election rival Kamala Harris pledged to work with Republicans to promote a united government, Trump delivered as divisive a speech as he has ever given, wildly exaggerating local tensions and misleading his audience about immigration statistics and policy.

"America is known, all throughout the world, as 'Occupied America.' They call it 'occupied.' We're being occupied by a criminal force," Trump thundered, in an 80-minute appearance in Aurora, Colorado, focused almost entirely on immigration.

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"But to everyone here in Colorado and all across our nation, I make this pledge and vow to you: November 5, 2024 will be Liberation Day in America," he added, flanked by posters of foreign suspected criminals.

While the US government has struggled for years to manage its southern border with Mexico, Trump has super-charged concerns by claiming an "invasion" is underway by migrants he says will rape and murder Americans.

Aurora was the scene of a viral video, played on a loop in right-wing media, showing armed Latinos rampaging through an apartment building.

The incident spurred sweeping, false narratives about the town in the Denver suburbs being terrorized by Latin American migrants – fueling Trump's election message that the US is overrun by what he calls "savages" and "animals."

Smearing Harris as a "criminal," Trump said falsely that Venezuelan gangs in Colorado had been given permission to shoot police, and spoke darkly of an "enemy within" that he defined as "all the scum that we have to deal with that hate our country."

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If Harris got four years in office, Trump said, "you would have 200 million people come in... the country would be over."

Trump vowed to tackle migrant gangs using the Alien Enemies Act of 1798 – which allows the federal government to round up and deport foreigners belonging to a country with which America is at war – as part of a mass deportation drive he christened "Operation Aurora."

Violent crime, which spiked under Trump, has, in fact, fallen in every year of the Biden administration.

Migrants commit fewer crimes proportionately than the native population, though migrant suspects have been named in a few high-profile cases of violent attacks on women and children, infuriating many Republican voters.

Undocumented immigration numbers at the southern border are now about where they were in 2020, the last year of Trump's presidency, after peaking at 250,000 migrant crossings in the month of December 2023.

Harris, campaigning in Scottsdale, Arizona, provided a marked contrast to Trump as she pushed a message of unity, pledging to institute a "bipartisan council of advisors" in addition to having a Republican in her cabinet.

"In the last several years in our country, there are some powerful forces that are trying to divide us as Americans, would cheer us on if we point fingers at each other," she said, adding: "We have more in common than what separates us."

With less than four weeks to the November 5 election, polls show a race too close to call. The latest Wall Street Journal poll Friday gave Harris slim leads in four of the seven swing states, but all the key contests are within the margin of error.

Aurora's police department told AFP this week that it had only isolated reports of activity in the city by the Venezuelan street gang called Tren de Aragua.

And the Republican mayor, Mike Coffman, called Trump's claims "grossly exaggerated," offering to give him a tour of Aurora, which he called a "safe city – not a city overrun by Venezuelan gangs."

However, Trump clearly believes his fearmongering is striking a chord.

He has similarly promoted the entirely fictitious story that Haitian migrants in Springfield, Ohio, are eating residents' cats and dogs.

In Aurora, he repeated his threat to deport the community, which is in Ohio legally, saying they "have to go back where they came from."