Trump said if a country, such as China, does not help to curb the flow of immigrants into the US, “we have these things called tariffs”.

Trump warned if other countries do not help to reduce it, then he could “tariff the hell out of that country” if re-elected.

Border security and immigration have emerged as top issues for Americans in the run-up to the November 5 election where Trump will face US President Joe Biden, a Democrat, in a rematch of their 2020 White House contest.

It was Trump’s first campaign event since a Manhattan jury on May 30 found him guilty on all 34 counts he faced of falsifying business records to cover up a US$130,000 payment his former lawyer Michael Cohen made to adult film actress Stormy Daniels before the 2016 election for her silence about a sexual encounter she says they had.

Trump has denied any wrongdoing and vowed to appeal the verdict. On Thursday he called the trial “rigged”.

Trump lambasted Biden’s latest effort to crack down on people crossing America’s southern border illegally, an asylum ban similar to restrictions Trump tried to implement when he was president.

Biden took executive action on Tuesday that instituted a broad asylum ban on migrants caught illegally crossing the US-Mexico border.

Trump claimed Biden’s new plan was “outrageous” and a concession of “death and defeat” at the border, even though the Biden measure mirrored Trump-era policies to deter would-be migrants.

Biden has toughened his approach to border security as immigration has emerged as a major political problem for him.

Trump made a hardline stance on immigration a centrepiece of his administration and has vowed a wide-ranging crackdown if reelected.

Under Biden’s order, migrants caught crossing illegally could be quickly deported or turned back to Mexico under the measure, which took effect on Wednesday.

There are exceptions for unaccompanied children, people who face serious medical or safety threats and victims of trafficking, the US Department of Homeland Security said.

Trump called Biden’s measure “bull****”, eliciting a chant of “bull****” from his friendly audience in Phoenix. Trump said he would rescind Biden’s measure on his first day in office if reelected.

Trump claimed without evidence that Biden’s asylum ban would allow a minimum of 2 million “illegal alien border crossers” into the US each year.

Asked how Trump reached that figure, Trump’s campaign did not immediately respond.

US Border Patrol arrested some 2 million migrants crossing illegally in the financial year ending September 30, 2023, and the country has seen similar figures this year. But Biden’s latest move aims to reduce attempted crossings, not maintain current levels.

Trump also said he could move US troops stationed abroad back home to patrol the southern border.

Biden has pushed unsuccessfully for months to pass a Senate bill crafted by a bipartisan group that would toughen border security but Republicans rejected it after Trump opposed it.

Kevin Munoz, a Biden campaign spokesman, said in a statement: “Donald Trump blocked the toughest, fairest bipartisan border legislation in a generation. He did it because he thinks it will help him politically”. Munoz added Trump’s role in killing the bill allows him to claim the immigration system is “broken”.

Several people were seen being taken out on stretchers from Trump’s event due to heat exhaustion after lining up for hours in temperatures approaching 43 degrees Celsius (110 Fahrenheit).