U.S. Customs and Border Protection officials said 10 immigrants were rescued after they were found hidden in a truck, and in another case dozens of immigrants were found stashed held in an apartment.

The 10 immigrants who were discovered hiding behind a false wall in a commercial moving truck Monday were rescued at the Falfurrias checkpoint, officials said.

Authorities said the rescue happened when a man who is a U.S. citizen approached the checkpoint on U.S. Highway 281 in a commercial moving truck.

During an immigration inspection, a border patrol K-9 alerted to the cargo area of the vehicle. Authorities said the driver claimed the vehicle was empty and when agents opened the cargo area, it initially appeared that was the case.

However, upon further inspection, agents discovered a false wall in the cargo area, behind which the 10 immigrants were hiding, CBP officials said. Once freed from the compartment, the immigrants were offered medical attention.

The truck driver was arrested and the case was turned over to the RGV Sector Prosecutions Office. CBP officials said he has an extensive criminal record, including convictions for drug possession, battery, felon in possession of a firearm, burglary and driving under the influence.

On Tuesday, Border Patrol agents arrested 31 illegal immigrants who were being held in a small apartment by an alleged human smuggler, according to CBP officials.

"Human smugglers are callous individuals who prey upon the desperation of immigrants," Chief Patrol Agent Manuel Padilla Jr. said. "Often times they will cram immigrants into small stash houses under deplorable, unsanitary conditions without adequate access to food and water for several days. Human smugglers are reckless individuals who use tactics that place the lives of immigrants and the general public in extreme danger."

Authorities said the immigrants arrested are from Mexico, El Salvador, Guatemala and Honduras.

A woman who is a Mexican national was also arrested for her apparent role as the caretaker of the stash house, CBP officials said. Her case has been referred to the RGV Sector Prosecutions Office.