SAN DIEGO -- Agents of the U.S. Border Patrol and Immigration and Customs Enforcement discovered another border tunnel Thursday about 1.5 miles west of the San Ysidro Port of Entry, according to ICE spokesperson, Lauren Mack.

Agents with the San Diego Tunnel Task Force found the unfinished 53-foot tunnel reinforced with a plywood roof and two-by-four wooden planks, Mack said.

Inside the tunnel, agents also found lights that operated with car batteries, fans and tubing for ventilation, Mack said.

According to an ICE news release, the tunnel diggers entered into the U.S. through a manhole in Tijuana about five feet south of the U.S. Mexico border, crawled under the border fence and accessed a sewage pipe.

After crawling for approximately 700 feet in the U.S., they broke out of the pipe and dug a 20-foot tunnel to reach the ground level, exiting into a open field, which was found covered with an old sofa cushion.

Agents worked closely with a contract construction company and a robot to help them conduct the search.

Agents from the task force believe the tunnel was being built to smuggle both humans and drugs from Tijuana to San Diego, Mack said.

More than 100 tunnels have been discovered along the U.S/Mexico border to date, Mack said. The majority were found on the California Mexico border.