Around 30 unaccompanied minors were smuggled into the U.S. after tunneling beneath the border wall near San Luis, Arizona on Monday together with a group of over 300 Central American migrants who then surrendered themselves to the Border Patrol.

The tunnels – a few feet long – were reportedly dug by smugglers under the steel border fence, letting hundreds of supposed asylum seekers enter the U.S, according to the Customs and Border Protection.

MIGRANT CARAVAN FREELY CROSSES MEXICAN BORDER AFTER GATES WERE LEFT OPEN, AUTHORITIES AVOIDED 'CONFRONTATION'

The migrants shortly surrendered to the authorities and requested asylum. The agency said that 179 of the record 376 people who crossed the border illegally were children, with over 30 of them being unaccompanied minors.

The group is believed to be the largest one yet to cross the border in a bid to get asylum in the U.S. The agency noted that smugglers often try to transport large groups of people and instruct them to cross the border and voluntarily surrender.

“In my 30 years with the Border Patrol, I have not been part of arresting a group of 376 people,” CBP Yuma Border Sector Chief Anthony Porvaznik told ABC News. “That’s really unheard of.”

In the case of this particular group, since most of the migrants were with their parents, they are supposed to be released into the U.S. while they wait for the government to process their asylum applications – a law many say only encourages illegal immigration.

The Trump administration previously tried to implement a new rule that would ban migrants from requesting asylum if they illegally cross the border in a bid to encourage applying to asylum outside the U.S.

The policy was shot down by a federal judge in November following uproar from Democrats and civil rights organizations.

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Porvaznik said that only “a change in the law” will help to solve the problem of illegal immigration. “The only reason they're trying to say that they're family units is that they know if they're a family unit, they're going to be released within 20 days.”

The crossing comes amid a political showdown in Washington, D.C., where President Trump has been sparring with Congressional Democrats over funding for the border wall, leaving the government closed for 28 days now.

The White House wants over $5 billion for the border wall, but Democrats have so far refused to cave in to the demands, President Trump's signature campaign issue.

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President Trump on Friday wrote in a tweet that he’ll make “a major announcement” Saturday afternoon concerning the ongoing partial government shutdown and the “humanitarian crisis” on the southern border.

But despite a recent surge in asylum-seeking families from Central America in recent months, the data indicated that border arrests remain low by historical standards.

The Border Patrol made 396,579 arrests on the Mexican border in the 2018 fiscal year, up 30 percent from a 46-year low during the same period a year earlier but still well below a high of more than 1.6 million in 2000.