CAMPO, Calif. -- Border Patrol agents discovered 61 Mexican nationals inside a tractor-trailer during a vehicle stop on eastbound Interstate 8, 10News reported.

The discovered happened Saturday night on I-8 near the Kitchen Creek Road exit, according to a Border Patrol news release.

Agents stopped the truck at about 9:15 p.m. and interviewed the driver, who admitted he was in the country illegally, officials said.

Agents searched the trailer and found 61 people hidden behind bales of cardboard, according to officials.

A modified trap door, possibly used as an entry door, was found at the floor of the trailer, agents said.

Agents seized the truck and the driver, a 29-year-old male Mexican national, is being prosecuted on charges of alien smuggling, officials said.