The illegal immigration situation at America's southern border is nearly unprecedented, a top Homeland Security official says.

During a White House call with reporters Thursday evening, acting Department of Homeland Security Secretary Kevin McAleenan said the Border Patrol is apprehending several thousand people every day.

"The situation is both a humanitarian and border security crisis that has become a national emergency," McAleenan said.

McAleenan, who was appointed to lead DHS on an acting basis when his predecessor Kirstjen Nielsen was ousted in April, then rattled off some staggering numbers:

On average, more than 4,500 people have illegally crossed into the U.S. or arrived at ports of entry without proper documentation over the past 21 days. That number was 700 in May 2017.

The current month will see the highest number of illegal migrant crossings in more than 12 years and is on pace to "significantly surpass" the record of 109,000 people, recorded in April.

More than 80,000 people are in custody, including 2,350 unaccompanied children. Both of those figures are record highs.

More than 75,000 families have arrived at the U.S. border with Mexico this month.

"Let me clear, the current situation is risking the lives of children every day," McAleenan said. "To address this crisis, Mexico must take significant action to secure their southern border, stop the unlawful flow of migrants across their territory, and attack the criminal groups preying on vulnerable migrants and profiting from these smuggling enterprises."

Earlier Thursday evening, President Donald Trump said he will institute increasing tariffs on Mexican goods until the country is able to stop the flow of migrants to the U.S. border.

Trump's trade adviser Peter Navarro, meanwhile, called Mexico a "criminal enterprise" for the "export … of illegal aliens."