Federal investigators said they found a more than 1,700-foot-long drug-smuggling tunnel connecting San Diego to Tijuana, Mexico, and authorities charged six people for conspiracy to distribute more than 1,750 pounds of cocaine.

The tunnel, which is about one-third of a mile long, is estimated to be 4 feet in diameter and 61 feet deep, according to the U.S. attorney’s office for the Southern District of California. It has a ventilation system, reinforced walls, electricity and a rail system.

Authorities also seized 3.5 pounds of heroin and 164 pounds of methamphetamine, according to the U.S. attorney’s office.

“There is no more light at the end of this narco-tunnel,” U.S. Attorney Randy Grossman said in a statement. “We will take down every subterranean smuggling route we find to keep illicit drugs from reaching our streets and destroying our families and communities.”

The opening of a cross-border tunnel between Tijuana, Mexico and San Diego.

Photo: Elliot Spagat/Associated Press

The U.S. attorney’s office said Monday that the tunnel was discovered Friday when Homeland Security Investigations officials were watching a residence that had been used for cocaine smuggling. 

Authorities were later led to a warehouse that sits about 300 feet north of the U.S.-Mexico border fence, the U.S. attorney’s office said. When authorities searched it, they found the exit point from the tunnel that was carved out of a concrete floor.

Since 1993, 90 subterranean passages have been found in the district, most recently in March 2020, according to ​​the U.S. attorney’s office. 

In the 1980s, the drug cartel of Mexican drug lord Joaquín “El Chapo” Guzmán used an underground tunnel that stretched from Arizona to Mexico. The entrance on the Mexico side of the tunnel was covered by a pool table. U.S. law enforcement found that tunnel in 1990.

Write to Allison Prang at allison.prang@wsj.com