TIJUANA, Mexico (AFP) - Nine people in Mexico were caught red handed on Tuesday digging a tunnel that was apparently to be used to sneak drugs into California, officials said.

The detainees had been digging from inside a house in the northwest border town of Tijuana and tried in vain to flee, the National Defense secretariat said.

The tunnel was about 20 metres underground and reachable by climbing down a ladder through a closet in the house.

Army troops also seized a truck that the detainees had been using to take away soil from the digging operations.

Mexican drug traffickers use a variety of techniques to try to smuggle drugs into the United States, from undocumented migrants carrying it in backpacks to catapults to sophisticated tunnels.

On January 22, a US-bound drone carrying 3kg of an unspecified drug crashed at a shopping centre in Tijuana.