A gang of armed thieves stole about 20 million pesos ($1 million) from an armoured truck that was about to load the money onto a plane at an international airport in central Mexico, authorities and reports said.

The brazen robbery took place Wednesday night when an armed gang in a van evaded security at Guanajuato International Airport, the state attorney's office said.

An initial report from the authorities said "armed individuals threatened cargo personnel and robbed them" of sacks of cash in a robbery that took just three minutes, although it did not confirm the amount stolen. Local reports said they made off with about 20 million pesos.

In a later statement, airport operator Grupo Aeroportuario del Pacífico said the gang of hooded and armed thieves broke through the perimeter fence to carry out the robbery before escaping by knocking down a different section of the fence.

On December 14, a truck with 118 million pesos ($6.2 million) on board was intercepted in southeast Guanajuato and the money stolen.

The vehicle was found buried in a nearby town.

Guanajuato is one of Mexico's most important industrial centres with a concentration of large international manufacturers of automobiles, planes and other heavy industry.

These activities, as well as the presence of important energy infrastructure, have attracted criminal organisations which engage in activities such as extortion, kidnapping and stealing fuel, according to authorities.