U.S. and Mexican authorities have discovered an unusually long and well-built tunnel running from the Mexican town of Tijuana to just across the border in California.

Officials on both sides of the border said about two tons of marijuana were found inside the tunnel.

Many tunnels have been found recently beneath the U.S.-Mexico border, but officials say this was one of the best-constructed and, at about one kilometer, one of the longest. The Associated Press says the tunnel included a cement-lined floor, lighting, and fresh-air vents.

AP reports the U.S. Attorney's office in San Diego, California, has opened a criminal investigation.

Some information for this report was provided by AFP and AP.