(CNN) -- Mexican soldiers have discovered a so-called "narco-tunnel" in Baja California that extends under the U.S. border, Mexican military officials said Friday.
The unfinished tunnel is 298 meters (977 feet) long, two meters (6.5 feet) high and about half that wide, and is thought to be intended for smuggling drugs, the National Defense Secretariat said.
Ten people, including one woman, were arrested as they were excavating, the agency said. Tools were also confiscated from the site.
The tunnel, which started inside a house and has lighting and ventilation, is thought to have started a year ago. Mexican military personnel came across it around 6 a.m. Friday, said Gen. Alfonso Duarte.
"They were approximately 100 meters (109 yards) into American territory," Duarte told reporters. "They had already crossed (into the U.S.), but they had no exit."
A small altar near the entrance to the tunnel contained figures for Santa Muerte -- the saint of death, who numerous U.S. government documents note has been adopted by drug traffickers as a "patron saint" -- and paraphernalia for using crystal methadone. One image above the altar read, "A prayer to protect the business."
The tunnel was discovered in a neighborhood near the airport in the border city of Tijuana after a resident raised an alarm, military officials said.
Mexico's Baja California neighbors the U.S. state of California.
CNN's Claudia Dominguez and Elizabeth Joseph and journalist Vicente Calderon contributed to this report.
