A group of 376 Central American migrants illegally crossed into the U.S. on Monday by crawling underneath a border fence in Yuma, Arizona, and immediately surrendered themselves to U.S. authorities.

Yuma Sector Border Patrol say they were “inundated” by the single largest group of migrant families and unaccompanied minors to cross in the area.

Group of 376 Central Americans illegally crossed from Mexico and inundated agents in #Yumasector on Monday morning. Almost all were families or unaccompanied juveniles. #NationalSecurity #SouthwestBorder pic.twitter.com/dWzS0LCgCV — CBP Arizona (@CBPArizona) January 18, 2019

Almost all of the group was made up of families and unaccompanied minors primarily from Guatemala. The illegal crossing occurred approximately 4.5 miles east of San Luis, Arizona.

The migrants gave no resistance and formed an orderly line while waiting to be processed, according to videos released by the CBP Friday. A Yuma Border Patrol spokesperson said that smugglers dug seven holes under the border barrier in Arizona. Those responsible have not been arrested, according to CBP local reporting.

“The United States Border Patrol is constantly building intelligence in order to combat these trafficking organizations that are constantly targeting them and gaining intelligence in order to apprehend them in the future,” said Jose Garibay, Yuma Sector Border Patrol public information officer. “They know that if you travel with a child, or there’s a child with you when you cross, then you have to be released within 20 days.”

Garibay further explained the reason the migrant groups are growing in numbers is they have figured out immigration system loopholes governing large groups with unaccompanied minors therein.

Due to the large size of the migrant group, CBP personnel from the surrounding locations were summoned to assist the local agents.

Robert Arce is a retired Phoenix Police detective with extensive experience working Mexican organized crime and street gangs. Arce has worked in the Balkans, Iraq, Haiti, and recently completed a three-year assignment in Monterrey, Mexico, working out of the Consulate for the United States Department of State, International Narcotics and Law Enforcement Program, where he was the Regional Program Manager for Northeast Mexico (Coahuila, Tamaulipas, Nuevo Leon, Durango, San Luis Potosi, Zacatecas.)