Three armed thieves in Mexico City hid their faces while robbing watches from a department store by wearing the blue surgical masks which are now ubiquitous in the flu-hit city.

Employees and security guards at a branch of the Sanborns department store told the daily Excelsior newspaper that the thieves were able to slip through the shop on Sunday without attracting attention, as they blended into a sea of masked shoppers.

One of the robbers threatened store assistants with a gun while another guarded the door and the third helped himself to watches from the jewelry department.

Banks in the Mexican capital have been forced to abandon normal rules over not letting in customers wearing face coverings

Faced with the flu outbreak, which has killed up to 149 people and triggered a major global health scare, government took emergency measures over the weekend and advised residents in the crowded city to wear face masks at all times outside their homes.