A tractor-trailer packed with illegal immigrants was discovered after a routine immigration stop by U.S. Border Patrol agents in southern California on Monday.

Border Patrol agents assigned to the El Centro Sector stopped a tractor-trailer as it approached the immigration checkpoint on Highway 86 in southern California at about 9:15 p.m. on Monday night. Agents searched the back of the refrigerated trailer and discovered 30 illegal immigrants hidden among the truck’s cargo, according to information obtained by Breitbart Texas from U.S. Customs and Border Protection officials.

The 30 illegal immigrants were determined to be Mexican citizens by Border Patrol agents during processing. They had been locked inside the trailer and had no way to get out in the event of an accident or being abandoned by their smuggler, officials stated.

“These arrests highlight the importance of our checkpoints. It also speaks to the outstanding and vigilant work that Border Patrol agents do on a daily basis to keep our country safe and protect human life,” Acting Chief Patrol Agent of the El Centro Sector Ryan J. Scudder said in a written statement.

The driver of the truck, also a Mexican citizen, was detained along with the 30 illegal immigrants. All 31 will be processed and removed, officials stated.

Just 12 days earlier, Breitbart Texas reported on El Centro Sector Border Patrol agents working the Highway 86 checkpoint discovered another 18-wheeler carrying 19 illegal immigrants from Mexico and Guatemala. The immigrants were also packed in a refrigerated trailer.

No mention was made about whether either driver will be prosecuted for human smuggling or driving the truck illegally with people inside the trailer compartment.

Illegal immigrants are frequently found locked in trailers. In 2003, the bodies of 18 illegal immigrants were found just south of Victoria, Texas, in an abandoned container. In May 2015, 18 more illegal immigrants were found inside yet another tractor-trailer, as reported by Breitbart Texas.

Bob Price serves as associate editor and senior political news contributor for Breitbart Texas. He is a founding member of the Breitbart Texas team. Follow him on Twitter @BobPriceBBTX.