
Mexican police have discovered a massive drug-smuggling tunnel 23 feet underground, leading from a building in the border city of Tijuana into the United States.

The 563-yard tunnel, which even had its own ventilation and lighting, was also fitted with rails that could be used to push cartloads of drugs through the three-foot-wide, four-foot-high hole to San Diego on the other side.

The discovery of the tunnel, which was attached to a house containing huge amounts of drugs, was made on Thursday, and confirmed Monday by the Mexican Attorney General's Office.

Going underground: A four-foot-high tunnel (pictured) found leading from a Tijuana building into San Diego was announced by the Mexican Attorney General's Office on Monday. It went as low as 23 feet under the earth

On rails: A rail track (pictured) was apparently used to move drugs along the tunnel. The building it originated from was found to contain 2.2 tons of marijuana after police raided it on a tip-off

The tunnel's entrance was located in La Hielera del Aeropuerto, a bottling and ice-making facility close to Tijuana's AL Rodriguez International Airport, according to The San Diego Tribune.

That building, located on Boulevard Cuauhtemoc around 330 yards from the US border, also contained 2.2 tons of marijuana in 371 packages, police said.

They had originally estimated five tons of marijuana on Thursday, before they obtained a court's permission to enter the home. They had been notified of the drugs by an anonymous tip-off.

US Immigration and Customs Enforcement Homeland Security has confirmed the existence of the tunnel, but has not said where exactly the San Diego entrance was located.

Tip-off: Police had been alerted to the building leading to the tunnel by an anonymous tip-off. Authorities have not said where in San Diego the tunnel ultimately comes out

Also Monday, federal police said they found 4.2 pounds of methamphetamine hidden in a wheel of cheese at a package delivery facility in Mexico City.

An X-ray inspection of the cheese block revealed a hidden package of drugs inside a sheet of lead and carbon paper.

The carbon paper was apparently intended to reduce any odor, while the lead may have been used to impede X-rays.

Another express delivery service, this one in the state of Jalisco, was found to have a package of 34 pounds of heroin.

Depending on how much it was cut, the heroin, which was found by sniffer dogs, could have supplied between 150,000 and 1.5million one-gram doses.

The office did not say whether the three finds were connected.