Washington DC - President Joe Biden is reportedly expected to announce tough curbs on migrant crossings over the Mexican border Tuesday as the issue weighs on his re-election chances against Donald Trump.

Biden is set to sign an executive order that would allow officials to deport migrants who cross illegally without processing their asylum claims first, several US media outlets reported on Monday.

The sweeping curbs, which Biden will reportedly launch at a ceremony at the White House along with mayors from border towns, would reportedly kick in whenever migrant crossings surge.

A White House official declined to confirm the reports.

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"From day one, the administration has always evaluated what actions could be taken. There haven't been any final decisions regarding what additional executive actions, if any, could be taken," the official told AFP.

Record numbers of border crossings during the Democrat's time in office have put huge pressure on Biden as he trails in most polls behind Republican former president Trump.

Republicans have sought to make the border a key issue ahead of the November 5 vote, portraying Biden as soft on stopping what Trump calls an "invasion" of migration.

More than 2.4 million migrants crossed the southern US border in 2023 alone, largely from Central America and Venezuela, as they flee poverty, violence, and disasters exacerbated by climate change.

The figure rose to a record high of 10,000 a day in December, and while it has fallen dramatically in recent months, polls show the issue is one of Biden's biggest liabilities in the election.

Biden's curbs would be some of the toughest brought in by any Democrat and would rely on the use of the same law that Trump's administration used to ban immigration from some Muslim countries.

But they would also almost certainly be challenged in court.

The White House blamed Republicans in Congress for blocking billions of dollars in funding for the border, which Biden tried to push through along with money for Ukraine and Israel.

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"Congressional Republicans do not care about securing the border or fixing America's broken immigration system," a White House spokesperson said in a statement.

"The administration continues to explore a series of policy options, and we remain committed to taking action to address our broken immigration system."

Trump has meanwhile ramped up his anti-immigration rhetoric as he seeks a White House comeback despite a historic court verdict last week that made him the first former president to become a convicted felon.

He has repeatedly spoken of migrants "poisoning the blood" of the US and railed, without evidence, about migrants from "insane asylums" flooding into the US.