"Six men armed with shotguns" were allowed admission in the early hours Sunday to the Compania Mexicana de Traslado de Valores security firm's depot, claiming to be working for the company, a state justice official told AFP on condition of anonymity.

According to company reports, the depot was holding 157 million pesos in cash during that time period money being held for other companies ahead of depositing in a bank.

With no suspects in the case, an investigation into the robbery has opened.