Republicans in the United States were set to warn, on Wednesday, that immigration has become a "humanitarian disaster", as homeland security officials braced for dramatic increases in already record-breaking numbers.

Crossings from Mexico have increased in recent weeks, according to two memos circulated by the party leadership, and President Joe Biden has allegedly made the current border crisis "the worst in American history."

A group of Republican senators has called a news conference to discuss what they see as Biden's border weakness, which they hope to portray as out of control ahead of the November midterm elections.

"This is a disaster of huge proportions, a humanitarian disaster. It's a public health disaster," Texas Senator John Cornyn, who is leading the effort, said as part of a panel discussion in San Antonio on Monday.

"And the Biden administration doesn't seem to care."

According to the Republican memos obtained by Politico, border officials expect to announce in the coming days that encounters have surpassed one million for the first six months of the new fiscal year.

Republicans are predicting a larger surge if Biden ends Title 42, a Trump policy implemented during the pandemic that allows border authorities to quickly deport asylum seekers and other migrants.

Read more: Title 42 applies to all migrants into the US, but not Ukrainians

Biden's own Democratic Party is divided, with progressives urging the President to repeal Title 42 while moderates warn that such a move would be disastrous in the absence of a firm plan to deal with an influx of asylum seekers.

Human Rights First reported earlier this month that Title 42 expulsions had resulted in nearly 10,000 reports of kidnapping, torture, rape, and other violent attacks against people detained or sent back to Mexico.

Kennji Kizuka, the group's associate director for refugee protection research, said the reports represented "just a tiny fraction" of the true cost of the "nightmarish policy".

"The grave human rights abuses faced by people turned away under Title 42 continue to mount every day that the Biden administration evades refugee law by using this illegal and inhumane policy," she concluded.