Reuters reported that three contractors were killed while working on the construction of a ventilation duct at a zinc mine in central Mexico owned by Industrias Penoles.

Miner and metals processor Penoles, which runs the world's largest primary silver producer, Fresnillo, operates the Tizapa mine in the central State of Mexico in the tiny municipality of Zacazonapan.

Penoles said that three other contractors also employed by Mineria Castellana were injured and are being treated at a local hospital. The miner could not say if the incident was an explosion but added that an investigation was underway.

The company said that the Tizapa mine produces mostly zinc although smaller quantities of lead, copper, silver and gold can also be found in the area.

Mr Christian Gomez a spokesman at the mine said that some 900 people including contractors work at the mine, situated about two hours from the state capital of Toluca. It was not immediately clear how many of those workers were miners.

In August, the Mexican government suspended work at 32 small coal mines in the northern state of Coahuila due to safety concerns after 13 miners died in the space of three weeks.