Harris vows migration crackdown, reform as she finally visits border

Kamala Harris pledged Friday she would tighten the border and fix America's broken immigration system on her first visit to the US-Mexico frontier as a presidential candidate.

The US vice president is playing catch-up on immigration, with a majority of Americans saying they trust Republican rival Donald Trump more than her on one of the most important issues for voters ahead of November's election.

In a speech in Douglas, Arizona before a friendly audience, Harris tried to straddle a tough-on-illegal-migration line with a promise to reach across the aisle to fix an immigration system she said was broken.

"The United States is a sovereign nation, and I believe we have a duty to set rules at our border and to enforce them, and I take that responsibility very seriously," she said.

"We are also a nation of immigrants... and so we must reform our immigration system to ensure that it works in an orderly way, that it is humane and that it makes our country stronger."

Harris said as president she would revive a bipartisan border bill Trump "tanked" last year, which would add 1,500 border agents and pay for 100 machines to detect smuggled fentanyl, a synthetic opioid ravaging US communities.

And she said anyone crossing the border illegally would be barred from seeking asylum in the country.

But "hard-working migrants" who come to the US legally should be given a pathway to citizenship, she said.

"I reject the false choice that suggests we must either choose between securing our border or creating a system of immigration that is safe, orderly and humane. We can and we must do both."

She said Trump, who has repeatedly demonised immigrants as murderers, rapists and mentally ill people, is "fanning the flames of fear and division."

"The American people deserve a president who cares more about border security than playing political games and their personal political future."

Harris earlier visited the border wall in Douglas, where she met with Border Patrol officials and was photographed alongside the distinctive metal slats.

It was her first visit to the frontier since Joe Biden ceded the Democratic Party nomination to her, and Republicans have hammered her for staying away.

Arizona is one of the half-dozen battleground states expected to decide the agonizingly close November 5 election, and it is where polls show Harris may have to do the most work.